test(instruction): extract constants

This makes the test code easier to follow

1 files changed, 274 insertions, 238 deletions

diff --git a/src/cpu/instruction.spec.ts b/src/cpu/instruction.spec.ts
index 2312f6c..0bf71bd 100644
--- a/src/cpu/instruction.spec.ts
+++ b/src/cpu/instruction.spec.ts
@@ -2,6 +2,45 @@ import { CPU } from './cpu';
 import { avrInstruction } from './instruction';
 import { assemble } from '../utils/assembler';
 
+const r0 = 0;
+const r1 = 1;
+const r2 = 2;
+const r3 = 3;
+const r4 = 4;
+const r5 = 5;
+const r6 = 6;
+const r7 = 7;
+const r8 = 8;
+const r16 = 16;
+const r17 = 17;
+const r18 = 18;
+const r19 = 19;
+const r20 = 20;
+const r21 = 21;
+const r22 = 22;
+const r23 = 23;
+const r24 = 24;
+const r26 = 26;
+const r27 = 27;
+const r31 = 31;
+const X = 26;
+const Y = 28;
+const Z = 30;
+const RAMPZ = 59;
+const EIND = 60;
+const SP = 93;
+const SPH = 94;
+const SREG = 95;
+
+// SREG Bits: I-HSVNZC
+const SREG_C = 0b00000001;
+const SREG_Z = 0b00000010;
+const SREG_N = 0b00000100;
+const SREG_V = 0b00001000;
+const SREG_S = 0b00010000;
+const SREG_H = 0b00100000;
+const SREG_I = 0b10000000;
+
 describe('avrInstruction', () => {
   let cpu: CPU;
 
@@ -19,51 +58,51 @@ describe('avrInstruction', () => {
 
   it('should execute `ADC r0, r1` instruction when carry is on', () => {
     loadProgram('ADC r0, r1');
-    cpu.data[0] = 10; // r0 <- 10
-    cpu.data[1] = 20; // r1 <- 20
-    cpu.data[95] = 0b00000001; // SREG <- -------C
+    cpu.data[r0] = 10;
+    cpu.data[r1] = 20;
+    cpu.data[SREG] = SREG_C;
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(1);
     expect(cpu.cycles).toEqual(1);
-    expect(cpu.data[0]).toEqual(31);
-    expect(cpu.data[95]).toEqual(0); // SREG: --------
+    expect(cpu.data[r0]).toEqual(31);
+    expect(cpu.data[SREG]).toEqual(0);
   });
 
   it('should execute `ADC r0, r1` instruction when carry is on and the result overflows', () => {
     loadProgram('ADC r0, r1');
-    cpu.data[0] = 10; // r0 <- 10
-    cpu.data[1] = 245; // r1 <- 20
-    cpu.data[95] = 0b00000001; // SREG <- -------C
+    cpu.data[r0] = 10;
+    cpu.data[r1] = 245;
+    cpu.data[SREG] = SREG_C;
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(1);
     expect(cpu.cycles).toEqual(1);
-    expect(cpu.data[0]).toEqual(0);
-    expect(cpu.data[95]).toEqual(0b00100011); // SREG: --H---ZC
+    expect(cpu.data[r0]).toEqual(0);
+    expect(cpu.data[SREG]).toEqual(SREG_H | SREG_Z | SREG_C);
   });
 
   it('should execute `BCLR 2` instruction', () => {
     loadProgram('BCLR 2');
-    cpu.data[95] = 0xff; // SREG <- 0xff
+    cpu.data[SREG] = 0xff;
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(1);
     expect(cpu.cycles).toEqual(1);
-    expect(cpu.data[95]).toEqual(0xfb);
+    expect(cpu.data[SREG]).toEqual(0xfb);
   });
 
   it('should execute `BLD r4, 7` instruction', () => {
     loadProgram('BLD r4, 7');
-    cpu.data[4] = 0x15; // r <- 0x15
-    cpu.data[95] = 0x40; // SREG <- 0x40
+    cpu.data[r4] = 0x15;
+    cpu.data[SREG] = 0x40;
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(1);
     expect(cpu.cycles).toEqual(1);
-    expect(cpu.data[4]).toEqual(0x95);
-    expect(cpu.data[95]).toEqual(0x40);
+    expect(cpu.data[r4]).toEqual(0x95);
+    expect(cpu.data[SREG]).toEqual(0x40);
   });
 
   it('should execute `BRBC 0, +8` instruction when SREG.C is clear', () => {
     loadProgram('BRBC 0, +8');
-    cpu.data[95] = 0b00001000; // SREG: V
+    cpu.data[SREG] = SREG_V;
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(1 + 8 / 2);
     expect(cpu.cycles).toEqual(2);
@@ -71,7 +110,7 @@ describe('avrInstruction', () => {
 
   it('should execute `BRBC 0, +8` instruction when SREG.C is set', () => {
     loadProgram('BRBC 0, +8');
-    cpu.data[95] = 0b00000001; // SREG: C
+    cpu.data[SREG] = SREG_C;
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(1);
     expect(cpu.cycles).toEqual(1);
@@ -79,7 +118,7 @@ describe('avrInstruction', () => {
 
   it('should execute `BRBS 3, 92` instruction when SREG.V is set', () => {
     loadProgram('BRBS 3, 92');
-    cpu.data[95] = 0b00001000; // SREG: V
+    cpu.data[SREG] = SREG_V;
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(1 + 92 / 2);
     expect(cpu.cycles).toEqual(2);
@@ -87,7 +126,7 @@ describe('avrInstruction', () => {
 
   it('should execute `BRBS 3, -4` instruction when SREG.V is set', () => {
     loadProgram('BRBS 3, -4');
-    cpu.data[95] = 0b00001000; // SREG: V
+    cpu.data[SREG] = SREG_V;
     avrInstruction(cpu);
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(0);
@@ -96,7 +135,7 @@ describe('avrInstruction', () => {
 
   it('should execute `BRBS 3, -4` instruction when SREG.V is clear', () => {
     loadProgram('BRBS 3, -4');
-    cpu.data[95] = 0x0; // SREG <- 0x0
+    cpu.data[SREG] = 0x0;
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(1);
     expect(cpu.cycles).toEqual(1);
@@ -113,61 +152,61 @@ describe('avrInstruction', () => {
 
   it('should execute `CALL` instruction', () => {
     loadProgram('CALL 0xb8');
-    cpu.data[94] = 0;
-    cpu.data[93] = 150; // SP <- 50
+    cpu.data[SPH] = 0;
+    cpu.data[SP] = 150;
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(0x5c);
     expect(cpu.cycles).toEqual(4);
     expect(cpu.data[150]).toEqual(2); // return addr
-    expect(cpu.data[93]).toEqual(148); // SP should be decremented
+    expect(cpu.data[SP]).toEqual(148); // SP should be decremented
   });
 
   it('should push 3-byte return address when executing `CALL` instruction on device with >128k flash', () => {
     cpu = new CPU(new Uint16Array(0x20000));
     loadProgram('CALL 0xb8');
-    cpu.data[94] = 0;
-    cpu.data[93] = 150; // SP <- 50
+    cpu.data[SPH] = 0;
+    cpu.data[SP] = 150;
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(0x5c);
     expect(cpu.cycles).toEqual(5);
     expect(cpu.data[150]).toEqual(2); // return addr
-    expect(cpu.data[93]).toEqual(147); // SP should be decremented by 3
+    expect(cpu.data[SP]).toEqual(147); // SP should be decremented by 3
   });
 
   it('should execute `CPC r27, r18` instruction', () => {
     loadProgram('CPC r27, r18');
-    cpu.data[18] = 0x1;
-    cpu.data[27] = 0x1;
+    cpu.data[r18] = 0x1;
+    cpu.data[r27] = 0x1;
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(1);
     expect(cpu.cycles).toEqual(1);
-    expect(cpu.data[95]).toEqual(0); // SREG clear
+    expect(cpu.data[SREG]).toEqual(0);
   });
 
   it('should execute `CPC r24, r1` instruction and set', () => {
     loadProgram('CPC r24, r1');
-    cpu.data[1] = 0; // r1 <- 0
-    cpu.data[24] = 0; // r24 <- 0
-    cpu.data[95] = 0b10000001; // SREG: I-------C
+    cpu.data[r1] = 0;
+    cpu.data[r24] = 0;
+    cpu.data[SREG] = SREG_I | SREG_C;
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(1);
     expect(cpu.cycles).toEqual(1);
-    expect(cpu.data[95]).toEqual(0b10110101); // SREG: I-HS-N-C
+    expect(cpu.data[SREG]).toEqual(SREG_I | SREG_H | SREG_S | SREG_N | SREG_C);
   });
 
   it('should execute `CPI r26, 0x9` instruction', () => {
     loadProgram('CPI r26, 0x9');
-    cpu.data[26] = 0x8;
+    cpu.data[r26] = 0x8;
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(1);
     expect(cpu.cycles).toEqual(1);
-    expect(cpu.data[95]).toEqual(0b00110101); // SREG: HSNC
+    expect(cpu.data[SREG]).toEqual(SREG_H | SREG_S | SREG_N | SREG_C);
   });
 
   it('should execute `CPSE r2, r3` when r2 != r3', () => {
     loadProgram('CPSE r2, r3');
-    cpu.data[2] = 10; // r2 <- 10
-    cpu.data[3] = 11; // r3 <- 11
+    cpu.data[r2] = 10;
+    cpu.data[r3] = 11;
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(1);
     expect(cpu.cycles).toEqual(1);
@@ -175,8 +214,8 @@ describe('avrInstruction', () => {
 
   it('should execute `CPSE r2, r3` when r2 == r3', () => {
     loadProgram('CPSE r2, r3');
-    cpu.data[2] = 10; // r2 <- 10
-    cpu.data[3] = 10; // r3 <- 10
+    cpu.data[r2] = 10;
+    cpu.data[r3] = 10;
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(2);
     expect(cpu.cycles).toEqual(2);
@@ -184,8 +223,8 @@ describe('avrInstruction', () => {
 
   it('should execute `CPSE r2, r3` when r2 == r3 and followed by 2-word instruction', () => {
     loadProgram('CPSE r2, r3', 'CALL 8');
-    cpu.data[2] = 10; // r2 <- 10
-    cpu.data[3] = 10; // r3 <- 10
+    cpu.data[r2] = 10;
+    cpu.data[r3] = 10;
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(3);
     expect(cpu.cycles).toEqual(3);
@@ -194,10 +233,10 @@ describe('avrInstruction', () => {
   it('should execute `EICALL` instruction', () => {
     cpu = new CPU(new Uint16Array(0x20000));
     loadProgram('EICALL');
-    cpu.data[94] = 0;
-    cpu.data[93] = 0x80;
-    cpu.data[0x3c] = 1; // EIND <- 1
-    cpu.dataView.setUint16(30, 0x1234, true); // Z <- 0x1234
+    cpu.data[SPH] = 0;
+    cpu.data[SP] = 0x80;
+    cpu.data[EIND] = 1;
+    cpu.dataView.setUint16(Z, 0x1234, true);
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(0x11234);
     expect(cpu.cycles).toEqual(4);
@@ -207,8 +246,8 @@ describe('avrInstruction', () => {
   it('should execute `EIJMP` instruction', () => {
     cpu = new CPU(new Uint16Array(0x20000));
     loadProgram('EIJMP');
-    cpu.data[0x3c] = 1; // EIND <- 1
-    cpu.dataView.setUint16(30, 0x1040, true); // Z <- 0x1040
+    cpu.data[EIND] = 1;
+    cpu.dataView.setUint16(Z, 0x1040, true);
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(0x11040);
     expect(cpu.cycles).toEqual(2);
@@ -217,11 +256,11 @@ describe('avrInstruction', () => {
   it('should execute `ELPM` instruction', () => {
     cpu = new CPU(new Uint16Array(0x20000));
     loadProgram('ELPM');
-    cpu.data[30] = 0x50; // Z <- 0x50
-    cpu.data[0x3b] = 0x2; // RAMPZ <- 2
+    cpu.data[Z] = 0x50;
+    cpu.data[RAMPZ] = 0x2;
     cpu.progBytes[0x20050] = 0x62; // value to be loaded
     avrInstruction(cpu);
-    expect(cpu.data[0]).toEqual(0x62); // check that value was loaded to r0
+    expect(cpu.data[r0]).toEqual(0x62); // check that value was loaded to r0
     expect(cpu.pc).toEqual(1);
     expect(cpu.cycles).toEqual(3);
   });
@@ -229,11 +268,11 @@ describe('avrInstruction', () => {
   it('should execute `ELPM r5, Z` instruction', () => {
     cpu = new CPU(new Uint16Array(0x20000));
     loadProgram('ELPM r5, Z');
-    cpu.data[30] = 0x11; // Z <- 0x11
-    cpu.data[0x3b] = 0x1; // RAMPZ <- 1
+    cpu.data[Z] = 0x11;
+    cpu.data[RAMPZ] = 0x1;
     cpu.progBytes[0x10011] = 0x99; // value to be loaded
     avrInstruction(cpu);
-    expect(cpu.data[5]).toEqual(0x99); // check that value was loaded to r5
+    expect(cpu.data[r5]).toEqual(0x99); // check that value was loaded to r5
     expect(cpu.pc).toEqual(1);
     expect(cpu.cycles).toEqual(3);
   });
@@ -241,57 +280,54 @@ describe('avrInstruction', () => {
   it('should execute `ELPM r6, Z+` instruction', () => {
     cpu = new CPU(new Uint16Array(0x20000));
     loadProgram('ELPM r6, Z+');
-    cpu.data[30] = 0xff; // Z <- 0xffff
-    cpu.data[31] = 0xff; // ...
-    cpu.data[0x3b] = 0x2; // RAMPZ <- 2
+    cpu.dataView.setUint16(Z, 0xffff, true);
+    cpu.data[RAMPZ] = 0x2;
     cpu.progBytes[0x2ffff] = 0x22; // value to be loaded
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(1);
     expect(cpu.cycles).toEqual(3);
-    expect(cpu.data[6]).toEqual(0x22); // check that value was loaded to r6
-    expect(cpu.data[30]).toEqual(0x0); // verify that Z was incremented
-    expect(cpu.data[31]).toEqual(0x0); // verify that Z was incremented
-    expect(cpu.data[0x3b]).toEqual(3); // verify that RAMPZ was incremented
+    expect(cpu.data[r6]).toEqual(0x22); // check that value was loaded to r6
+    expect(cpu.dataView.getUint16(Z, true)).toEqual(0x0); // verify that Z was incremented
+    expect(cpu.data[RAMPZ]).toEqual(3); // verify that RAMPZ was incremented
   });
 
   it('should clamp RAMPZ when executing `ELPM r6, Z+` instruction', () => {
     cpu = new CPU(new Uint16Array(0x20000));
     loadProgram('ELPM r6, Z+');
-    cpu.data[30] = 0xff; // Z <- 0xffff
-    cpu.data[31] = 0xff; // ...
-    cpu.data[0x3b] = 0x3; // RAMPZ <- 3
+    cpu.dataView.setUint16(Z, 0xffff, true);
+    cpu.data[RAMPZ] = 0x3;
     avrInstruction(cpu);
-    expect(cpu.data[0x3b]).toEqual(0x0); // verify that RAMPZ was reset to zero
+    expect(cpu.data[RAMPZ]).toEqual(0x0); // verify that RAMPZ was reset to zero
   });
 
   it('should execute `ICALL` instruction', () => {
     loadProgram('ICALL');
-    cpu.data[94] = 0;
-    cpu.data[93] = 0x80;
-    cpu.dataView.setUint16(30, 0x2020, true); // Z <- 0x2020
+    cpu.data[SPH] = 0;
+    cpu.data[SP] = 0x80;
+    cpu.dataView.setUint16(Z, 0x2020, true);
     avrInstruction(cpu);
     expect(cpu.cycles).toEqual(3);
     expect(cpu.pc).toEqual(0x2020);
     expect(cpu.data[0x80]).toEqual(1); // Return address
-    expect(cpu.data[93]).toEqual(0x7e); // SP Should decrement by 2
+    expect(cpu.data[SP]).toEqual(0x7e); // SP Should decrement by 2
   });
 
   it('should push 3-byte return address when executing `ICALL` instruction on device with >128k flash', () => {
     cpu = new CPU(new Uint16Array(0x20000));
     loadProgram('ICALL');
-    cpu.data[94] = 0;
-    cpu.data[93] = 0x80;
-    cpu.dataView.setUint16(30, 0x2020, true); // Z <- 0x2020
+    cpu.data[SPH] = 0;
+    cpu.data[SP] = 0x80;
+    cpu.dataView.setUint16(Z, 0x2020, true);
     avrInstruction(cpu);
     expect(cpu.cycles).toEqual(4);
     expect(cpu.pc).toEqual(0x2020);
     expect(cpu.data[0x80]).toEqual(1); // Return address
-    expect(cpu.data[93]).toEqual(0x7d); // SP Should decrement by 3
+    expect(cpu.data[SP]).toEqual(0x7d); // SP Should decrement by 3
   });
 
   it('should execute `IJMP` instruction', () => {
     loadProgram('IJMP');
-    cpu.dataView.setUint16(30, 0x1040, true); // Z <- 0x1040
+    cpu.dataView.setUint16(Z, 0x1040, true);
     avrInstruction(cpu);
     expect(cpu.cycles).toEqual(2);
     expect(cpu.pc).toEqual(0x1040);
@@ -303,27 +339,27 @@ describe('avrInstruction', () => {
     avrInstruction(cpu);
     expect(cpu.cycles).toEqual(1);
     expect(cpu.pc).toEqual(1);
-    expect(cpu.data[5]).toEqual(0xaf);
+    expect(cpu.data[r5]).toEqual(0xaf);
   });
 
   it('should execute `INC r5` instruction', () => {
     loadProgram('INC r5');
-    cpu.data[5] = 0x7f;
+    cpu.data[r5] = 0x7f;
     avrInstruction(cpu);
-    expect(cpu.data[5]).toEqual(0x80);
+    expect(cpu.data[r5]).toEqual(0x80);
     expect(cpu.pc).toEqual(1);
     expect(cpu.cycles).toEqual(1);
-    expect(cpu.data[95]).toEqual(0b00001100); // SREG: NV
+    expect(cpu.data[SREG]).toEqual(SREG_N | SREG_V);
   });
 
   it('should execute `INC r5` instruction when r5 == 0xff', () => {
     loadProgram('INC r5');
-    cpu.data[5] = 0xff;
+    cpu.data[r5] = 0xff;
     avrInstruction(cpu);
-    expect(cpu.data[5]).toEqual(0);
+    expect(cpu.data[r5]).toEqual(0);
     expect(cpu.pc).toEqual(1);
     expect(cpu.cycles).toEqual(1);
-    expect(cpu.data[95]).toEqual(0b00000010); // SREG: Z
+    expect(cpu.data[SREG]).toEqual(SREG_Z);
   });
 
   it('should execute `JMP 0xb8` instruction', () => {
@@ -335,40 +371,40 @@ describe('avrInstruction', () => {
 
   it('should execute `LAC Z, r19` instruction', () => {
     loadProgram('LAC Z, r19');
-    cpu.data[19] = 0x02; // r19 <- 0x02
-    cpu.dataView.setUint16(30, 0x100, true); // Z <- 0x100
+    cpu.data[r19] = 0x02;
+    cpu.dataView.setUint16(Z, 0x100, true);
     cpu.data[0x100] = 0x96;
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(1);
     expect(cpu.cycles).toEqual(1);
-    expect(cpu.data[19]).toEqual(0x96);
-    expect(cpu.dataView.getUint16(30, true)).toEqual(0x100);
+    expect(cpu.data[r19]).toEqual(0x96);
+    expect(cpu.dataView.getUint16(Z, true)).toEqual(0x100);
     expect(cpu.data[0x100]).toEqual(0x94);
   });
 
   it('should execute `LAS Z, r17` instruction', () => {
     loadProgram('LAS Z, r17');
-    cpu.data[17] = 0x11; // r17 <- 0x11
-    cpu.data[30] = 0x80; // Z <- 0x80
+    cpu.data[r17] = 0x11;
+    cpu.data[Z] = 0x80;
     cpu.data[0x80] = 0x44;
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(1);
     expect(cpu.cycles).toEqual(1);
-    expect(cpu.data[17]).toEqual(0x44);
-    expect(cpu.data[30]).toEqual(0x80);
+    expect(cpu.data[r17]).toEqual(0x44);
+    expect(cpu.data[Z]).toEqual(0x80);
     expect(cpu.data[0x80]).toEqual(0x55);
   });
 
   it('should execute `LAT Z, r0` instruction', () => {
     loadProgram('LAT Z, r0');
-    cpu.data[0] = 0x33; // r0 <- 0x33
-    cpu.data[30] = 0x80; // Z <- 0x80
+    cpu.data[r0] = 0x33;
+    cpu.data[Z] = 0x80;
     cpu.data[0x80] = 0x66;
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(1);
     expect(cpu.cycles).toEqual(1);
-    expect(cpu.data[0]).toEqual(0x66);
-    expect(cpu.data[30]).toEqual(0x80);
+    expect(cpu.data[r0]).toEqual(0x66);
+    expect(cpu.data[Z]).toEqual(0x80);
     expect(cpu.data[0x80]).toEqual(0x55);
   });
 
@@ -377,7 +413,7 @@ describe('avrInstruction', () => {
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(0x1);
     expect(cpu.cycles).toEqual(1);
-    expect(cpu.data[28]).toEqual(0xff);
+    expect(cpu.data[Y]).toEqual(0xff);
   });
 
   it('should execute `LDS r5, 0x150` instruction', () => {
@@ -386,256 +422,256 @@ describe('avrInstruction', () => {
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(0x2);
     expect(cpu.cycles).toEqual(2);
-    expect(cpu.data[5]).toEqual(0x7a);
+    expect(cpu.data[r5]).toEqual(0x7a);
   });
 
   it('should execute `LD r1, X` instruction', () => {
     loadProgram('LD r1, X');
     cpu.data[0xc0] = 0x15;
-    cpu.data[26] = 0xc0; // X <- 0xc0
+    cpu.data[X] = 0xc0;
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(1);
     expect(cpu.cycles).toEqual(2);
-    expect(cpu.data[1]).toEqual(0x15);
-    expect(cpu.data[26]).toEqual(0xc0); // verify that X was unchanged
+    expect(cpu.data[r1]).toEqual(0x15);
+    expect(cpu.data[X]).toEqual(0xc0); // verify that X was unchanged
   });
 
   it('should execute `LD r17, X+` instruction', () => {
     loadProgram('LD r17, X+');
     cpu.data[0xc0] = 0x15;
-    cpu.data[26] = 0xc0; // X <- 0xc0
+    cpu.data[X] = 0xc0;
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(1);
     expect(cpu.cycles).toEqual(2);
-    expect(cpu.data[17]).toEqual(0x15);
-    expect(cpu.data[26]).toEqual(0xc1); // verify that X was incremented
+    expect(cpu.data[r17]).toEqual(0x15);
+    expect(cpu.data[X]).toEqual(0xc1); // verify that X was incremented
   });
 
   it('should execute `LD r1, -X` instruction', () => {
     loadProgram('LD r1, -X');
     cpu.data[0x98] = 0x22;
-    cpu.data[26] = 0x99; // X <- 0x99
+    cpu.data[X] = 0x99;
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(1);
     expect(cpu.cycles).toEqual(2);
-    expect(cpu.data[1]).toEqual(0x22);
-    expect(cpu.data[26]).toEqual(0x98); // verify that X was decremented
+    expect(cpu.data[r1]).toEqual(0x22);
+    expect(cpu.data[X]).toEqual(0x98); // verify that X was decremented
   });
 
   it('should execute `LD r8, Y` instruction', () => {
     loadProgram('LD r8, Y');
     cpu.data[0xc0] = 0x15;
-    cpu.data[28] = 0xc0; // Y <- 0xc0
+    cpu.data[Y] = 0xc0;
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(1);
     expect(cpu.cycles).toEqual(2);
     expect(cpu.data[8]).toEqual(0x15);
-    expect(cpu.data[28]).toEqual(0xc0); // verify that Y was unchanged
+    expect(cpu.data[Y]).toEqual(0xc0); // verify that Y was unchanged
   });
 
   it('should execute `LD r3, Y+` instruction', () => {
     loadProgram('LD r3, Y+');
     cpu.data[0xc0] = 0x15;
-    cpu.data[28] = 0xc0; // Y <- 0xc0
+    cpu.data[Y] = 0xc0;
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(1);
     expect(cpu.cycles).toEqual(2);
-    expect(cpu.data[3]).toEqual(0x15);
-    expect(cpu.data[28]).toEqual(0xc1); // verify that Y was incremented
+    expect(cpu.data[r3]).toEqual(0x15);
+    expect(cpu.data[Y]).toEqual(0xc1); // verify that Y was incremented
   });
 
   it('should execute `LD r0, -Y` instruction', () => {
     loadProgram('LD r0, -Y');
     cpu.data[0x98] = 0x22;
-    cpu.data[28] = 0x99; // Y <- 0x99
+    cpu.data[Y] = 0x99;
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(1);
     expect(cpu.cycles).toEqual(2);
-    expect(cpu.data[0]).toEqual(0x22);
-    expect(cpu.data[28]).toEqual(0x98); // verify that Y was decremented
+    expect(cpu.data[r0]).toEqual(0x22);
+    expect(cpu.data[Y]).toEqual(0x98); // verify that Y was decremented
   });
 
   it('should execute `LDD r4, Y+2` instruction', () => {
     loadProgram('LDD r4, Y+2');
     cpu.data[0x82] = 0x33;
-    cpu.data[28] = 0x80; // Y <- 0x80
+    cpu.data[Y] = 0x80;
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(1);
     expect(cpu.cycles).toEqual(2);
-    expect(cpu.data[4]).toEqual(0x33);
-    expect(cpu.data[28]).toEqual(0x80); // verify that Y was unchanged
+    expect(cpu.data[r4]).toEqual(0x33);
+    expect(cpu.data[Y]).toEqual(0x80); // verify that Y was unchanged
   });
 
   it('should execute `LD r5, Z` instruction', () => {
     loadProgram('LD r5, Z');
     cpu.data[0xcc] = 0xf5;
-    cpu.data[30] = 0xcc; // Z <- 0xcc
+    cpu.data[Z] = 0xcc;
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(1);
     expect(cpu.cycles).toEqual(2);
-    expect(cpu.data[5]).toEqual(0xf5);
-    expect(cpu.data[30]).toEqual(0xcc); // verify that Z was unchanged
+    expect(cpu.data[r5]).toEqual(0xf5);
+    expect(cpu.data[Z]).toEqual(0xcc); // verify that Z was unchanged
   });
 
   it('should execute `LD r7, Z+` instruction', () => {
     loadProgram('LD r7, Z+');
     cpu.data[0xc0] = 0x25;
-    cpu.data[30] = 0xc0; // Z <- 0xc0
+    cpu.data[Z] = 0xc0;
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(1);
     expect(cpu.cycles).toEqual(2);
-    expect(cpu.data[7]).toEqual(0x25);
-    expect(cpu.data[30]).toEqual(0xc1); // verify that Y was incremented
+    expect(cpu.data[r7]).toEqual(0x25);
+    expect(cpu.data[Z]).toEqual(0xc1); // verify that Y was incremented
   });
 
   it('should execute `LD r0, -Z` instruction', () => {
     loadProgram('LD r0, -Z');
     cpu.data[0x9e] = 0x66;
-    cpu.data[30] = 0x9f; // Z <- 0x9f
+    cpu.data[Z] = 0x9f;
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(1);
     expect(cpu.cycles).toEqual(2);
-    expect(cpu.data[0]).toEqual(0x66);
-    expect(cpu.data[30]).toEqual(0x9e); // verify that Y was decremented
+    expect(cpu.data[r0]).toEqual(0x66);
+    expect(cpu.data[Z]).toEqual(0x9e); // verify that Y was decremented
   });
 
   it('should execute `LDD r15, Z+31` instruction', () => {
     loadProgram('LDD r15, Z+31');
     cpu.data[0x9f] = 0x33;
-    cpu.data[30] = 0x80; // Z <- 0x80
+    cpu.data[Z] = 0x80;
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(1);
     expect(cpu.cycles).toEqual(2);
     expect(cpu.data[15]).toEqual(0x33);
-    expect(cpu.data[30]).toEqual(0x80); // verify that Z was unchanged
+    expect(cpu.data[Z]).toEqual(0x80); // verify that Z was unchanged
   });
 
   it('should execute `LPM` instruction', () => {
     loadProgram('LPM');
     cpu.progMem[0x40] = 0xa0;
-    cpu.data[30] = 0x80; // Z <- 0x80
+    cpu.data[Z] = 0x80;
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(1);
     expect(cpu.cycles).toEqual(3);
-    expect(cpu.data[0]).toEqual(0xa0);
-    expect(cpu.data[30]).toEqual(0x80); // verify that Z was unchanged
+    expect(cpu.data[r0]).toEqual(0xa0);
+    expect(cpu.data[Z]).toEqual(0x80); // verify that Z was unchanged
   });
 
   it('should execute `LPM r2, Z` instruction', () => {
     loadProgram('LPM r2, Z');
     cpu.progMem[0x40] = 0xa0;
-    cpu.data[30] = 0x80; // Z <- 0x80
+    cpu.data[Z] = 0x80;
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(1);
     expect(cpu.cycles).toEqual(3);
-    expect(cpu.data[2]).toEqual(0xa0);
-    expect(cpu.data[30]).toEqual(0x80); // verify that Z was unchanged
+    expect(cpu.data[r2]).toEqual(0xa0);
+    expect(cpu.data[Z]).toEqual(0x80); // verify that Z was unchanged
   });
 
   it('should execute `LPM r1, Z+` instruction', () => {
     loadProgram('LPM r1, Z+');
     cpu.progMem[0x40] = 0xa0;
-    cpu.data[30] = 0x80; // Z <- 0x80
+    cpu.data[Z] = 0x80;
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(1);
     expect(cpu.cycles).toEqual(3);
-    expect(cpu.data[1]).toEqual(0xa0);
-    expect(cpu.data[30]).toEqual(0x81); // verify that Z was incremented
+    expect(cpu.data[r1]).toEqual(0xa0);
+    expect(cpu.data[Z]).toEqual(0x81); // verify that Z was incremented
   });
 
   it('should execute `LSR r7` instruction', () => {
     loadProgram('LSR r7');
-    cpu.data[7] = 0x45; // r7 <- 0x45
+    cpu.data[r7] = 0x45;
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(1);
     expect(cpu.cycles).toEqual(1);
-    expect(cpu.data[7]).toEqual(0x22);
-    expect(cpu.data[95]).toEqual(0b00011001); // SREG SVC
+    expect(cpu.data[r7]).toEqual(0x22);
+    expect(cpu.data[SREG]).toEqual(SREG_S | SREG_V | SREG_C);
   });
 
   it('should execute `MOV r7, r8` instruction', () => {
     loadProgram('MOV r7, r8');
-    cpu.data[8] = 0x45; // r7 <- 0x45
+    cpu.data[r8] = 0x45;
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(1);
     expect(cpu.cycles).toEqual(1);
-    expect(cpu.data[7]).toEqual(0x45);
+    expect(cpu.data[r7]).toEqual(0x45);
   });
 
   it('should execute `MOVW r26, r22` instruction', () => {
     loadProgram('MOVW r26, r22');
-    cpu.data[22] = 0x45; // r22 <- 0x45
-    cpu.data[23] = 0x9a; // r23 <- 0x9a
+    cpu.data[r22] = 0x45;
+    cpu.data[r23] = 0x9a;
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(1);
     expect(cpu.cycles).toEqual(1);
-    expect(cpu.data[26]).toEqual(0x45);
-    expect(cpu.data[27]).toEqual(0x9a);
+    expect(cpu.data[X]).toEqual(0x45);
+    expect(cpu.data[r27]).toEqual(0x9a);
   });
 
   it('should execute `MUL r5, r6` instruction', () => {
     loadProgram('MUL r5, r6');
-    cpu.data[5] = 100; // r5 <- 55
-    cpu.data[6] = 5; // r6 <- 5
+    cpu.data[r5] = 100;
+    cpu.data[r6] = 5;
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(1);
     expect(cpu.cycles).toEqual(2);
     expect(cpu.dataView.getUint16(0, true)).toEqual(500);
-    expect(cpu.data[95]).toEqual(0b0); // SREG: 0
+    expect(cpu.data[SREG]).toEqual(0);
   });
 
   it('should execute `MUL r5, r6` instruction and update carry flag when numbers are big', () => {
     loadProgram('MUL r5, r6');
-    cpu.data[5] = 200; // r5 <- 200
-    cpu.data[6] = 200; // r6 <- 200
+    cpu.data[r5] = 200;
+    cpu.data[r6] = 200;
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(1);
     expect(cpu.cycles).toEqual(2);
     expect(cpu.dataView.getUint16(0, true)).toEqual(40000);
-    expect(cpu.data[95]).toEqual(0b00000001); // SREG: C
+    expect(cpu.data[SREG]).toEqual(SREG_C);
   });
 
   it('should execute `MUL r0, r1` and update the zero flag', () => {
     loadProgram('MUL r0, r1');
-    cpu.data[0] = 0; // r0 <- 0
-    cpu.data[1] = 9; // r1 <- 9
+    cpu.data[r0] = 0;
+    cpu.data[r1] = 9;
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(1);
     expect(cpu.cycles).toEqual(2);
     expect(cpu.dataView.getUint16(0, true)).toEqual(0);
-    expect(cpu.data[95]).toEqual(0b00000010); // SREG: Z
+    expect(cpu.data[SREG]).toEqual(SREG_Z);
   });
 
   it('should execute `MULS r18, r19` instruction', () => {
     loadProgram('MULS r18, r19');
-    cpu.data[18] = -5; // r18 <- -5
-    cpu.data[19] = 100; // r19 <- 100
+    cpu.data[r18] = -5;
+    cpu.data[r19] = 100;
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(1);
     expect(cpu.cycles).toEqual(2);
     expect(cpu.dataView.getInt16(0, true)).toEqual(-500);
-    expect(cpu.data[95]).toEqual(0b00000001); // SREG: C
+    expect(cpu.data[SREG]).toEqual(SREG_C);
   });
 
   it('should execute `MULSU r16, r17` instruction', () => {
     loadProgram('MULSU r16, r17');
-    cpu.data[16] = -5; // r16 <- -5
-    cpu.data[17] = 200; // r17 <- 200
+    cpu.data[r16] = -5;
+    cpu.data[r17] = 200;
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(1);
     expect(cpu.cycles).toEqual(2);
     expect(cpu.dataView.getInt16(0, true)).toEqual(-1000);
-    expect(cpu.data[95]).toEqual(0b00000001); // SREG: C
+    expect(cpu.data[SREG]).toEqual(SREG_C);
   });
 
   it('should execute `NEG r20` instruction', () => {
     loadProgram('NEG r20');
-    cpu.data[20] = 0x56; // r20 <- 0x56
+    cpu.data[r20] = 0x56;
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(1);
     expect(cpu.cycles).toEqual(1);
     expect(cpu.data[20]).toEqual(0xaa);
-    expect(cpu.data[95]).toEqual(0b00010101); // SREG: NC
+    expect(cpu.data[SREG]).toEqual(SREG_S | SREG_N | SREG_C);
   });
 
   it('should execute `NOP` instruction', () => {
@@ -647,7 +683,7 @@ describe('avrInstruction', () => {
 
   it('should execute `OUT 0x3f, r1` instruction', () => {
     loadProgram('OUT 0x3f, r1');
-    cpu.data[1] = 0x5a; // r1 <- 0x5a
+    cpu.data[r1] = 0x5a;
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(0x1);
     expect(cpu.cycles).toEqual(1);
@@ -656,112 +692,112 @@ describe('avrInstruction', () => {
 
   it('should execute `POP r26` instruction', () => {
     loadProgram('POP r26');
-    cpu.data[94] = 0;
-    cpu.data[93] = 0xff; // SP <- 0xff
+    cpu.data[SPH] = 0;
+    cpu.data[SP] = 0xff;
     cpu.data[0x100] = 0x1a;
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(0x1);
     expect(cpu.cycles).toEqual(2);
-    expect(cpu.data[26]).toEqual(0x1a);
-    expect(cpu.dataView.getUint16(93, true)).toEqual(0x100); // SP
+    expect(cpu.data[X]).toEqual(0x1a);
+    expect(cpu.dataView.getUint16(SP, true)).toEqual(0x100);
   });
 
   it('should execute `PUSH r11` instruction', () => {
     loadProgram('PUSH r11');
     cpu.data[11] = 0x2a;
-    cpu.data[94] = 0;
-    cpu.data[93] = 0xff; // SP <- 0xff
+    cpu.data[SPH] = 0;
+    cpu.data[SP] = 0xff;
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(0x1);
     expect(cpu.cycles).toEqual(2);
     expect(cpu.data[0xff]).toEqual(0x2a);
-    expect(cpu.dataView.getUint16(93, true)).toEqual(0xfe); // SP
+    expect(cpu.dataView.getUint16(SP, true)).toEqual(0xfe);
   });
 
   it('should execute `RCALL .+6` instruction', () => {
     loadProgram('RCALL 6');
-    cpu.data[94] = 0;
-    cpu.data[93] = 0x80; // SP <- 0x80
+    cpu.data[SPH] = 0;
+    cpu.data[SP] = 0x80;
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(4);
     expect(cpu.cycles).toEqual(3);
     expect(cpu.dataView.getUint16(0x80, true)).toEqual(1); // RET address
-    expect(cpu.data[93]).toEqual(0x7e); // SP should decrement by 2
+    expect(cpu.data[SP]).toEqual(0x7e); // SP should decrement by 2
   });
 
   it('should execute `RCALL .-4` instruction', () => {
     loadProgram('NOP', 'RCALL -4');
-    cpu.data[94] = 0;
-    cpu.data[93] = 0x80; // SP <- 0x80
+    cpu.data[SPH] = 0;
+    cpu.data[SP] = 0x80;
     avrInstruction(cpu);
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(0);
     expect(cpu.cycles).toEqual(4); // 1 for NOP, 3 for RCALL
     expect(cpu.dataView.getUint16(0x80, true)).toEqual(2); // RET address
-    expect(cpu.data[93]).toEqual(0x7e); // SP should decrement by 2
+    expect(cpu.data[SP]).toEqual(0x7e); // SP should decrement by 2
   });
 
   it('should push 3-byte return address when executing `RCALL` instruction on device with >128k flash', () => {
     cpu = new CPU(new Uint16Array(0x20000));
     loadProgram('RCALL 6');
-    cpu.data[94] = 0;
-    cpu.data[93] = 0x80;
-    cpu.dataView.setUint16(30, 0x2020, true); // Z <- 0x2020
+    cpu.data[SPH] = 0;
+    cpu.data[SP] = 0x80;
+    cpu.dataView.setUint16(Z, 0x2020, true);
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(4);
     expect(cpu.cycles).toEqual(4);
     expect(cpu.dataView.getUint16(0x80, true)).toEqual(1); // RET address
-    expect(cpu.data[93]).toEqual(0x7d); // SP Should decrement by 3
+    expect(cpu.data[SP]).toEqual(0x7d); // SP Should decrement by 3
   });
 
   it('should execute `RET` instruction', () => {
     loadProgram('RET');
-    cpu.data[94] = 0;
-    cpu.data[93] = 0x90; // SP <- 0x90
+    cpu.data[SPH] = 0;
+    cpu.data[SP] = 0x90;
     cpu.data[0x92] = 16;
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(16);
     expect(cpu.cycles).toEqual(4);
-    expect(cpu.data[93]).toEqual(0x92); // SP should increment by 2
+    expect(cpu.data[SP]).toEqual(0x92); // SP should increment by 2
   });
 
   it('should execute `RET` instruction on device with >128k flash', () => {
     cpu = new CPU(new Uint16Array(0x20000));
     loadProgram('RET');
-    cpu.data[94] = 0;
-    cpu.data[93] = 0x90; // SP <- 0x90
+    cpu.data[SPH] = 0;
+    cpu.data[SP] = 0x90;
     cpu.data[0x91] = 0x1;
     cpu.data[0x93] = 0x16;
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(0x10016);
     expect(cpu.cycles).toEqual(5);
-    expect(cpu.data[93]).toEqual(0x93); // SP should increment by 3
+    expect(cpu.data[SP]).toEqual(0x93); // SP should increment by 3
   });
 
   it('should execute `RETI` instruction', () => {
     loadProgram('RETI');
-    cpu.data[94] = 0;
-    cpu.data[93] = 0xc0; // SP <- 0xc0
+    cpu.data[SPH] = 0;
+    cpu.data[SP] = 0xc0;
     cpu.data[0xc2] = 200;
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(200);
     expect(cpu.cycles).toEqual(4);
-    expect(cpu.data[93]).toEqual(0xc2); // SP should increment by 2
-    expect(cpu.data[95]).toEqual(0b10000000); // SREG: I
+    expect(cpu.data[SP]).toEqual(0xc2); // SP should increment by 2
+    expect(cpu.data[SREG]).toEqual(SREG_I);
   });
 
   it('should execute `RETI` instruction on device with >128k flash', () => {
     cpu = new CPU(new Uint16Array(0x20000));
     loadProgram('RETI');
-    cpu.data[94] = 0;
-    cpu.data[93] = 0xc0; // SP <- 0xc0
+    cpu.data[SPH] = 0;
+    cpu.data[SP] = 0xc0;
     cpu.data[0xc1] = 0x1;
     cpu.data[0xc3] = 0x30;
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(0x10030);
     expect(cpu.cycles).toEqual(5);
-    expect(cpu.data[93]).toEqual(0xc3); // SP should increment by 3
-    expect(cpu.data[95]).toEqual(0b10000000); // SREG: I
+    expect(cpu.data[SP]).toEqual(0xc3); // SP should increment by 3
+    expect(cpu.data[SREG]).toEqual(SREG_I);
   });
 
   it('should execute `RJMP 2` instruction', () => {
@@ -773,22 +809,22 @@ describe('avrInstruction', () => {
 
   it('should execute `ROR r0` instruction', () => {
     loadProgram('ROR r0');
-    cpu.data[0] = 0x11; // r0 <- 0x11
+    cpu.data[r0] = 0x11;
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(1);
     expect(cpu.cycles).toEqual(1);
-    expect(cpu.data[0]).toEqual(0x08); // r0 should be right-shifted
-    expect(cpu.data[95]).toEqual(0b00011001); // SREG: SVI
+    expect(cpu.data[r0]).toEqual(0x08); // r0 should be right-shifted
+    expect(cpu.data[SREG]).toEqual(SREG_S | SREG_V | SREG_C);
   });
 
   it('should execute `SBCI r23, 3`', () => {
     loadProgram('SBCI r23, 3');
-    cpu.data[23] = 3; // r23 <- 3
-    cpu.data[95] = 0b10000001; // SREG <- I------C
+    cpu.data[r23] = 3;
+    cpu.data[SREG] = SREG_I | SREG_C;
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(1);
     expect(cpu.cycles).toEqual(1);
-    expect(cpu.data[95]).toEqual(0b10110101); // SREG: I-HS-N-C
+    expect(cpu.data[SREG]).toEqual(SREG_I | SREG_H | SREG_S | SREG_N | SREG_C);
   });
 
   it('should execute `SBI 0x0c, 5`', () => {
@@ -826,7 +862,7 @@ describe('avrInstruction', () => {
 
   it('should execute `STS 0x151, r31` instruction', () => {
     loadProgram('STS 0x151, r31');
-    cpu.data[31] = 0x80; // r31 <- 0x80
+    cpu.data[r31] = 0x80;
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(2);
     expect(cpu.cycles).toEqual(2);
@@ -835,143 +871,143 @@ describe('avrInstruction', () => {
 
   it('should execute `ST X, r1` instruction', () => {
     loadProgram('ST X, r1');
-    cpu.data[1] = 0x5a; // r1 <- 0x5a
-    cpu.data[26] = 0x9a; // X <- 0x9a
+    cpu.data[r1] = 0x5a;
+    cpu.data[X] = 0x9a;
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(1);
     expect(cpu.cycles).toEqual(2);
     expect(cpu.data[0x9a]).toEqual(0x5a);
-    expect(cpu.data[26]).toEqual(0x9a); // verify that X was unchanged
+    expect(cpu.data[X]).toEqual(0x9a); // verify that X was unchanged
   });
 
   it('should execute `ST X+, r1` instruction', () => {
     loadProgram('ST X+, r1');
-    cpu.data[1] = 0x5a; // r1 <- 0x5a
-    cpu.data[26] = 0x9a; // X <- 0x9a
+    cpu.data[r1] = 0x5a;
+    cpu.data[X] = 0x9a;
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(1);
     expect(cpu.cycles).toEqual(2);
     expect(cpu.data[0x9a]).toEqual(0x5a);
-    expect(cpu.data[26]).toEqual(0x9b); // verify that X was incremented
+    expect(cpu.data[X]).toEqual(0x9b); // verify that X was incremented
   });
 
   it('should execute `ST -X, r17` instruction', () => {
     loadProgram('ST -X, r17');
-    cpu.data[17] = 0x88; // r17 <- 0x88
-    cpu.data[26] = 0x99; // X <- 0x99
+    cpu.data[r17] = 0x88;
+    cpu.data[X] = 0x99;
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(1);
     expect(cpu.cycles).toEqual(2);
     expect(cpu.data[0x98]).toEqual(0x88);
-    expect(cpu.data[26]).toEqual(0x98); // verify that X was decremented
+    expect(cpu.data[X]).toEqual(0x98); // verify that X was decremented
   });
 
   it('should execute `ST Y, r2` instruction', () => {
     loadProgram('ST Y, r2');
-    cpu.data[2] = 0x5b; // r2 <- 0x5b
-    cpu.data[28] = 0x9a; // Y <- 0x9a
+    cpu.data[r2] = 0x5b;
+    cpu.data[Y] = 0x9a;
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(1);
     expect(cpu.cycles).toEqual(2);
     expect(cpu.data[0x9a]).toEqual(0x5b);
-    expect(cpu.data[28]).toEqual(0x9a); // verify that Y was unchanged
+    expect(cpu.data[Y]).toEqual(0x9a); // verify that Y was unchanged
   });
 
   it('should execute `ST Y+, r1` instruction', () => {
     loadProgram('ST Y+, r1');
-    cpu.data[1] = 0x5a; // r1 <- 0x5a
-    cpu.data[28] = 0x9a; // Y <- 0x9a
+    cpu.data[r1] = 0x5a;
+    cpu.data[Y] = 0x9a;
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(1);
     expect(cpu.cycles).toEqual(2);
     expect(cpu.data[0x9a]).toEqual(0x5a);
-    expect(cpu.data[28]).toEqual(0x9b); // verify that Y was incremented
+    expect(cpu.data[Y]).toEqual(0x9b); // verify that Y was incremented
   });
 
   it('should execute `ST -Y, r1` instruction', () => {
     loadProgram('ST -Y, r1');
-    cpu.data[1] = 0x5a; // r1 <- 0x5a
-    cpu.data[28] = 0x9a; // Y <- 0x9a
+    cpu.data[r1] = 0x5a;
+    cpu.data[Y] = 0x9a;
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(1);
     expect(cpu.cycles).toEqual(2);
     expect(cpu.data[0x99]).toEqual(0x5a);
-    expect(cpu.data[28]).toEqual(0x99); // verify that Y was decremented
+    expect(cpu.data[Y]).toEqual(0x99); // verify that Y was decremented
   });
 
   it('should execute `STD Y+17, r0` instruction', () => {
     loadProgram('STD Y+17, r0');
-    cpu.data[0] = 0xba; // r0 <- 0xba
-    cpu.data[28] = 0x9a; // Y <- 0x9a
+    cpu.data[r0] = 0xba;
+    cpu.data[Y] = 0x9a;
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(1);
     expect(cpu.cycles).toEqual(2);
     expect(cpu.data[0x9a + 17]).toEqual(0xba);
-    expect(cpu.data[28]).toEqual(0x9a); // verify that Y was unchanged
+    expect(cpu.data[Y]).toEqual(0x9a); // verify that Y was unchanged
   });
 
   it('should execute `ST Z, r16` instruction', () => {
     loadProgram('ST Z, r16');
-    cpu.data[16] = 0xdf; // r2 <- 0xdf
-    cpu.data[30] = 0x40; // Z <- 0x40
+    cpu.data[r16] = 0xdf;
+    cpu.data[Z] = 0x40;
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(1);
     expect(cpu.cycles).toEqual(2);
     expect(cpu.data[0x40]).toEqual(0xdf);
-    expect(cpu.data[30]).toEqual(0x40); // verify that Z was unchanged
+    expect(cpu.data[Z]).toEqual(0x40); // verify that Z was unchanged
   });
 
   it('should execute `ST Z+, r0` instruction', () => {
     loadProgram('ST Z+, r0');
-    cpu.data[0] = 0x55; // r0 <- 0x55
-    cpu.dataView.setUint16(30, 0x155, true); // Z <- 0x155
+    cpu.data[r0] = 0x55;
+    cpu.dataView.setUint16(Z, 0x155, true);
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(1);
     expect(cpu.cycles).toEqual(2);
     expect(cpu.data[0x155]).toEqual(0x55);
-    expect(cpu.dataView.getUint16(30, true)).toEqual(0x156); // verify that Z was incremented
+    expect(cpu.dataView.getUint16(Z, true)).toEqual(0x156); // verify that Z was incremented
   });
 
   it('should execute `ST -Z, r16` instruction', () => {
     loadProgram('ST -Z, r16');
-    cpu.data[16] = 0x5a; // r16 <- 0x5a
-    cpu.data[30] = 0xff; // Z <- 0xff
+    cpu.data[r16] = 0x5a;
+    cpu.data[Z] = 0xff;
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(1);
     expect(cpu.cycles).toEqual(2);
     expect(cpu.data[0xfe]).toEqual(0x5a);
-    expect(cpu.data[30]).toEqual(0xfe); // verify that Z was decremented
+    expect(cpu.data[Z]).toEqual(0xfe); // verify that Z was decremented
   });
 
   it('should execute `STD Z+1, r0` instruction', () => {
     loadProgram('STD Z+1, r0');
-    cpu.data[0] = 0xcc; // r0 <- 0xcc
-    cpu.data[30] = 0x50; // Z <- 0x50
+    cpu.data[r0] = 0xcc;
+    cpu.data[Z] = 0x50;
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(1);
     expect(cpu.cycles).toEqual(2);
     expect(cpu.data[0x51]).toEqual(0xcc);
-    expect(cpu.data[30]).toEqual(0x50); // verify that Z was unchanged
+    expect(cpu.data[Z]).toEqual(0x50); // verify that Z was unchanged
   });
 
   it('should execute `SWAP r1` instruction', () => {
     loadProgram('SWAP r1');
-    cpu.data[1] = 0xa5; // r1 <- 0xa5
+    cpu.data[r1] = 0xa5;
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(1);
     expect(cpu.cycles).toEqual(1);
-    expect(cpu.data[1]).toEqual(0x5a); // r1
+    expect(cpu.data[r1]).toEqual(0x5a);
   });
 
   it('should execute `XCH Z, r21` instruction', () => {
     loadProgram('XCH Z, r21');
-    cpu.data[21] = 0xa1; // r21 <- 0xa1
-    cpu.data[30] = 0x50; // Z <- 0x50
+    cpu.data[r21] = 0xa1;
+    cpu.data[Z] = 0x50;
     cpu.data[0x50] = 0xb9;
     avrInstruction(cpu);
     expect(cpu.pc).toEqual(1);
     expect(cpu.cycles).toEqual(1);
-    expect(cpu.data[21]).toEqual(0xb9); // r21
+    expect(cpu.data[r21]).toEqual(0xb9);
     expect(cpu.data[0x50]).toEqual(0xa1);
   });
 });