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psyqo: make fixed-point iDiv/dDiv constexpr #2048

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psyqo: make fixed-point iDiv/dDiv constexpr #2048

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45 changes: 43 additions & 2 deletions src/mips/psyqo/fixed-point.hh
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Original file line number Diff line number Diff line change
Expand Up @@ -37,10 +37,51 @@ namespace psyqo {

namespace FixedPointInternals {

uint32_t iDiv(uint64_t rem, uint32_t base, unsigned scale);
int32_t dDiv(int32_t a, int32_t b, unsigned scale);
void printInt(uint32_t value, const eastl::function<void(char)>&, unsigned scale);

constexpr uint32_t iDiv(uint64_t rem, uint32_t base, unsigned scale) {
rem *= scale;
uint64_t b = base;
uint64_t res, d = 1;
uint32_t high = rem >> 32;

res = 0;
if (high >= base) {
high /= base;
res = static_cast<uint64_t>(high) << 32;
rem -= static_cast<uint64_t>(high * base) << 32;
}

while (static_cast<int64_t>(b) > 0 && b < rem) {
b = b + b;
d = d + d;
}

do {
if (rem >= b) {
rem -= b;
res += d;
}
b >>= 1;
d >>= 1;
} while (d);

return res;
}

constexpr int32_t dDiv(int32_t a, int32_t b, unsigned scale) {
int s = 1;
if (a < 0) {
a = -a;
s = -1;
}
if (b < 0) {
b = -b;
s = -s;
}
return iDiv(a, b, scale) * s;
}
Comment on lines +72 to +83

@coderabbitai coderabbitai Bot Jul 8, 2026

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🎯 Functional Correctness | 🟡 Minor | ⚡ Quick win

🧩 Analysis chain

🏁 Script executed:

#!/bin/bash
# Find compile-time (constexpr/consteval) usages that could feed dDiv with signed division.
rg -nP -C3 '\bdDiv\s*\(' src/mips/psyqo
# Look for constexpr/consteval contexts invoking FixedPoint division on signed 32-bit types.
rg -nP -C3 'operator/|operator/=' src/mips/psyqo/fixed-point.hh

Repository: grumpycoders/pcsx-redux

Length of output: 3784

🏁 Script executed:

#!/bin/bash
set -euo pipefail

# Inspect the relevant parts of fixed-point.hh around dDiv and the signed operators.
sed -n '1,140p' src/mips/psyqo/fixed-point.hh
printf '\n---\n'
sed -n '300,430p' src/mips/psyqo/fixed-point.hh
printf '\n---\n'
sed -n '470,520p' src/mips/psyqo/fixed-point.hh

Repository: grumpycoders/pcsx-redux

Length of output: 10563

🏁 Script executed:

#!/bin/bash
set -euo pipefail

# Find constructors, raw accessors, and any direct uses of INT32_MIN / numeric_limits in the fixed-point implementation.
rg -n -C2 'raw\(|INT32_MIN|numeric_limits|FixedPoint\s*\(|constexpr\s+FixedPoint' src/mips/psyqo/fixed-point.hh

Repository: grumpycoders/pcsx-redux

Length of output: 6974

Guard INT32_MIN before negating in dDiv

FixedPoint::operator/ and operator/= for signed 32-bit values call this directly, so a raw INT32_MIN still makes constant evaluation ill-formed when a = -a; or b = -b;. Widen the temporary or special-case the minimum value.

🤖 Prompt for AI Agents 
Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@src/mips/psyqo/fixed-point.hh` around lines 72 - 83, The dDiv helper in
fixed-point.hh negates signed inputs directly, which still breaks when a or b is
INT32_MIN. Update dDiv (used by FixedPoint::operator/ and
FixedPoint::operator/=) to guard the minimum 32-bit value before negation,
either by widening to a larger temporary type or by special-casing INT32_MIN so
constant evaluation remains valid.


} // namespace FixedPointInternals

/**
Expand Down
42 changes: 0 additions & 42 deletions src/mips/psyqo/src/fixed-point.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -26,48 +26,6 @@ SOFTWARE.

#include "psyqo/fixed-point.hh"

uint32_t psyqo::FixedPointInternals::iDiv(uint64_t rem, uint32_t base, unsigned scale) {
rem *= scale;
uint64_t b = base;
uint64_t res, d = 1;
uint32_t high = rem >> 32;

res = 0;
if (high >= base) {
high /= base;
res = static_cast<uint64_t>(high) << 32;
rem -= static_cast<uint64_t>(high * base) << 32;
}

while (static_cast<int64_t>(b) > 0 && b < rem) {
b = b + b;
d = d + d;
}

do {
if (rem >= b) {
rem -= b;
res += d;
}
b >>= 1;
d >>= 1;
} while (d);

return res;
}

int32_t psyqo::FixedPointInternals::dDiv(int32_t a, int32_t b, unsigned scale) {
int s = 1;
if (a < 0) {
a = -a;
s = -1;
}
if (b < 0) {
b = -b;
s = -s;
}
return iDiv(a, b, scale) * s;
}

void psyqo::FixedPointInternals::printInt(uint32_t value, const eastl::function<void(char)>& charPrinter,
unsigned scale) {
Expand Down
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