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Fix round_coordinate behavior for arm64 (fixes Namco System 22 video issues on arm64) #14369

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Merged
merged 5 commits into from
Oct 19, 2025
Merged

Fix round_coordinate behavior for arm64 (fixes Namco System 22 video issues on arm64) #14369

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f4b640c
Fix round_coordinate behavior for arm64
seleuco Oct 19, 2025
30719fa
Modernize code and fix indentation
seleuco Oct 19, 2025
1905330
poly.h: Safer
cuavas Oct 19, 2025
f47958e
video/poly.h: Dumb syntax error.
cuavas Oct 19, 2025
b6f6fcc
video/poly.h: Remove another stray tab.
cuavas Oct 19, 2025
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20 changes: 14 additions & 6 deletions src/devices/video/poly.h
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Original file line number Diff line number Diff line change
Expand Up @@ -37,8 +37,9 @@

#pragma once

#include <climits>
#include <atomic>
#include <climits>
#include <limits>


#define KEEP_POLY_STATISTICS 0
Expand Down Expand Up @@ -365,12 +366,19 @@ class poly_manager
using unit_array = poly_array<work_unit, 0>;

// round in a cross-platform consistent manner
inline int32_t round_coordinate(BaseType value)
static int32_t round_coordinate(BaseType value)
{
int32_t result = int32_t(std::floor(value));
if (value > 0 && result < 0)
return INT_MAX - 1;
return result + (value - BaseType(result) > BaseType(0.5));
// saturate (avoid overflow/underflow)
if (value >= BaseType(std::numeric_limits<int32_t>::max()))
return std::numeric_limits<int32_t>::max();
Comment on lines +372 to +373
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You know that if it doesn’t hit this test, int32_t(ipart) will never give std::numeric_limits<int32_t>::max(), because std::floor always produces a lesser or equal value, and converting to integer rounds towards zero.

In cases where BaseType can't represent std::numeric_limits<int32_t>::max() precisely, BaseType(std::numeric_limits<int32_t>::max()) gets rounded away from zero so the test should still be safe.

const BaseType ipart = std::floor(value);
if (ipart < BaseType(std::numeric_limits<int32_t>::min()))
return std::numeric_limits<int32_t>::min();
Comment on lines +374 to +376
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This needs to be < not <= or it will fail to round when BaseType can precisely represent a 32-bit integer and ipart == BaseType(std::numeric_limits<int32_t>::min()) and fpart > BaseType(0.5).


// round
// TODO: this rounds the midpoint towards negative infinity - should it use more standard behaviour?
const BaseType fpart = value - ipart;
return int32_t(ipart) + ((fpart > BaseType(0.5)) ? 1 : 0);
}

// internal helpers
Expand Down