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chore: use if-else when decoding THUMB instructions

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This commit is contained in:
Rekai Nyangadzayi Musuka
2022-02-02 18:35:19 -04:00
parent c2901ee0d8
commit 045c98de1f
1 changed files with 39 additions and 55 deletions
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94
src/cpu.zig
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@@ -424,60 +424,45 @@ pub fn checkCond(cpsr: PSR, cond: u4) bool {
fn thumbPopulate() [0x400]ThumbInstrFn {
return comptime {
@setEvalBranchQuota(0xC00);
@setEvalBranchQuota(0x5000);
var lut = [_]ThumbInstrFn{thumbUndefined} ** 0x400;
var i: usize = 0;
while (i < lut.len) : (i += 1) {
if (i >> 7 & 0x7 == 0b000) {
const op = i >> 5 & 0x3;
const offset = i & 0x1F;
lut[i] = format1(op, offset);
}
if (i >> 5 & 0x1F == 0b00011) {
const I = i >> 4 & 1 == 1;
const is_sub = i >> 3 & 1 == 1;
const rn = i & 0x7;
lut[i] = format2(I, is_sub, rn);
}
if (i >> 7 & 0x7 == 0b001) {
const op = i >> 5 & 0x3;
const rd = i >> 2 & 0x7;
lut[i] = format3(op, rd);
}
if (i >> 4 & 0x3F == 0b010000) {
const op = i & 0xF;
lut[i] = format4(op);
}
if (i >> 4 & 0x3F == 0b010001) {
} else if (i >> 4 & 0x3F == 0b010001) {
const op = i >> 2 & 0x3;
const h1 = i >> 1 & 1;
const h2 = i & 1;
lut[i] = format5(op, h1, h2);
}
} else if (i >> 5 & 0x1F == 0b00011) {
const I = i >> 4 & 1 == 1;
const is_sub = i >> 3 & 1 == 1;
const rn = i & 0x7;
if (i >> 5 & 0x1F == 0b01001) {
lut[i] = format2(I, is_sub, rn);
} else if (i >> 5 & 0x1F == 0b01001) {
const rd = i >> 2 & 0x7;
lut[i] = format6(rd);
}
if (i >> 6 & 0xF == 0b1000) {
const L = i >> 5 & 1 == 1;
} else if (i >> 6 & 0xF == 0b0101) {
// TODO: Format 7 and Format 8
lut[i] = thumbUndefined;
} else if (i >> 7 & 0x7 == 0b000) {
const op = i >> 5 & 0x3;
const offset = i & 0x1F;
lut[i] = format10(L, offset);
}
lut[i] = format1(op, offset);
} else if (i >> 7 & 0x7 == 0b001) {
const op = i >> 5 & 0x3;
const rd = i >> 2 & 0x7;
if (i >> 7 & 0x7 == 0b011) {
lut[i] = format3(op, rd);
} else if (i >> 7 & 0x7 == 0b011) {
const B = i >> 6 & 1 == 1;
const L = i >> 5 & 1 == 1;
const offset = i & 0x1F;
@@ -485,44 +470,43 @@ fn thumbPopulate() [0x400]ThumbInstrFn {
lut[i] = format9(B, L, offset);
}
if (i >> 6 & 0xF == 0b1010) {
const isSP = i >> 5 & 1 == 1;
const rd = i >> 2 & 0x7;
lut[i] = format12(isSP, rd);
}
if (i >> 2 & 0xFF == 0xB0) {
const S = i >> 1 & 1 == 1;
lut[i] = format13(S);
}
} else if (i >> 2 & 0xFF == 0xDF) {
// Format 17 | Software Interrupt
lut[i] = thumbUndefined;
} else if (i >> 6 & 0xF == 0b1000) {
const L = i >> 5 & 1 == 1;
const offset = i & 0x1F;
if (i >> 6 & 0xF == 0b1011 and i >> 3 & 0x3 == 0b10) {
lut[i] = format10(L, offset);
} else if (i >> 6 & 0xF == 0b1001) {
// Format 11 | SP-relative load / store
lut[i] = thumbUndefined;
} else if (i >> 6 & 0xF == 0b1010) {
const isSP = i >> 5 & 1 == 1;
const rd = i >> 2 & 0x7;
lut[i] = format12(isSP, rd);
} else if (i >> 6 & 0xF == 0b1011 and i >> 3 & 0x3 == 0b10) {
const L = i >> 5 & 1 == 1;
const R = i >> 2 & 1 == 1;
lut[i] = format14(L, R);
}
if (i >> 6 & 0xF == 0b1100) {
} else if (i >> 6 & 0xF == 0b1100) {
const L = i >> 5 & 1 == 1;
const rb = i >> 2 & 0x7;
lut[i] = format15(L, rb);
}
if (i >> 6 & 0xF == 0b1101) {
} else if (i >> 6 & 0xF == 0b1101) {
const cond = i >> 2 & 0xF;
lut[i] = format16(cond);
}
if (i >> 5 & 0x1F == 0b11100) {
} else if (i >> 5 & 0x1F == 0b11100) {
lut[i] = format18();
}
if (i >> 6 & 0xF == 0b1111) {
} else if (i >> 6 & 0xF == 0b1111) {
const is_low = i >> 5 & 1 == 1;
lut[i] = format19(is_low);