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Fixed timer overflow on some platforms

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We have an implementation that uses 128-bit math and one that handles large values without it (thanks @jessechounard and @rabbit-ecl!)

Fixes https://github.com/libsdl-org/SDL/issues/15042
This commit is contained in:
Sam Lantinga
2026-02-25 10:21:20 -08:00
parent 0246598d62
commit 24404d9047
1 changed files with 28 additions and 6 deletions
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src/timer/SDL_timer.c
+28 -6
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@@ -535,11 +535,20 @@ bool SDL_RemoveTimer(SDL_TimerID id)
#endif // !SDL_PLATFORM_EMSCRIPTEN #endif // !SDL_PLATFORM_EMSCRIPTEN
#ifdef USE_128BIT_MATH
typedef unsigned __int128 Uint128;
#endif
static Uint64 tick_start; static Uint64 tick_start;
#ifdef USE_128BIT_MATH
static Uint128 tick_numerator_ns;
static Uint128 tick_numerator_ms;
#else
static Uint32 tick_numerator_ns; static Uint32 tick_numerator_ns;
static Uint32 tick_denominator_ns; static Uint32 tick_denominator_ns;
static Uint32 tick_numerator_ms; static Uint32 tick_numerator_ms;
static Uint32 tick_denominator_ms; static Uint32 tick_denominator_ms;
#endif
#if defined(SDL_TIMER_WINDOWS) && !defined(SDL_PLATFORM_XBOXONE) && !defined(SDL_PLATFORM_XBOXSERIES) #if defined(SDL_TIMER_WINDOWS) && !defined(SDL_PLATFORM_XBOXONE) && !defined(SDL_PLATFORM_XBOXSERIES)
#include <mmsystem.h> #include <mmsystem.h>
@@ -583,7 +592,9 @@ static void SDLCALL SDL_TimerResolutionChanged(void *userdata, const char *name,
void SDL_InitTicks(void) void SDL_InitTicks(void)
{ {
Uint64 tick_freq; Uint64 tick_freq;
#ifndef USE_128BIT_MATH
Uint32 gcd; Uint32 gcd;
#endif
if (tick_start) { if (tick_start) {
return; return;
@@ -597,6 +608,10 @@ void SDL_InitTicks(void)
tick_freq = SDL_GetPerformanceFrequency(); tick_freq = SDL_GetPerformanceFrequency();
SDL_assert(tick_freq > 0 && tick_freq <= (Uint64)SDL_MAX_UINT32); SDL_assert(tick_freq > 0 && tick_freq <= (Uint64)SDL_MAX_UINT32);
#ifdef USE_128BIT_MATH
tick_numerator_ns = ((Uint128)SDL_NS_PER_SECOND << 32) / tick_freq;
tick_numerator_ms = ((Uint128)SDL_MS_PER_SECOND << 32) / tick_freq;
#else
gcd = SDL_CalculateGCD(SDL_NS_PER_SECOND, (Uint32)tick_freq); gcd = SDL_CalculateGCD(SDL_NS_PER_SECOND, (Uint32)tick_freq);
tick_numerator_ns = (SDL_NS_PER_SECOND / gcd); tick_numerator_ns = (SDL_NS_PER_SECOND / gcd);
tick_denominator_ns = (Uint32)(tick_freq / gcd); tick_denominator_ns = (Uint32)(tick_freq / gcd);
@@ -604,6 +619,7 @@ void SDL_InitTicks(void)
gcd = SDL_CalculateGCD(SDL_MS_PER_SECOND, (Uint32)tick_freq); gcd = SDL_CalculateGCD(SDL_MS_PER_SECOND, (Uint32)tick_freq);
tick_numerator_ms = (SDL_MS_PER_SECOND / gcd); tick_numerator_ms = (SDL_MS_PER_SECOND / gcd);
tick_denominator_ms = (Uint32)(tick_freq / gcd); tick_denominator_ms = (Uint32)(tick_freq / gcd);
#endif
tick_start = SDL_GetPerformanceCounter(); tick_start = SDL_GetPerformanceCounter();
if (!tick_start) { if (!tick_start) {
@@ -630,9 +646,12 @@ Uint64 SDL_GetTicksNS(void)
} }
starting_value = (SDL_GetPerformanceCounter() - tick_start); starting_value = (SDL_GetPerformanceCounter() - tick_start);
value = (starting_value * tick_numerator_ns); #ifdef USE_128BIT_MATH
SDL_assert(value >= starting_value); value = (Uint64)(((Uint128)starting_value * tick_numerator_ns) >> 32);
value /= tick_denominator_ns; #else
value = (starting_value / tick_denominator_ns) * tick_numerator_ns +
(starting_value % tick_denominator_ns) * tick_numerator_ns / tick_denominator_ns;
#endif
return value; return value;
} }
@@ -645,9 +664,12 @@ Uint64 SDL_GetTicks(void)
} }
starting_value = (SDL_GetPerformanceCounter() - tick_start); starting_value = (SDL_GetPerformanceCounter() - tick_start);
value = (starting_value * tick_numerator_ms); #ifdef USE_128BIT_MATH
SDL_assert(value >= starting_value); value = (Uint64)(((Uint128)starting_value * tick_numerator_ms) >> 32);
value /= tick_denominator_ms; #else
value = (starting_value / tick_denominator_ms) * tick_numerator_ms +
(starting_value % tick_denominator_ms) * tick_numerator_ms / tick_denominator_ms;
#endif
return value; return value;
} }