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Use 64-bit file seeks on Windows #4456

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Merged
zcbenz merged 2 commits into from
Sep 8, 2026
+27 −7
Merged

Use 64-bit file seeks on Windows #4456

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cb47e8d
Use 64-bit file seeks on Windows
dhiltgen Jun 1, 2026
5a14153
Remove tests since it is too slow and change is trival
zcbenz Sep 8, 2026
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34 changes: 27 additions & 7 deletions mlx/io/load.h
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Original file line number Diff line number Diff line change
Expand Up @@ -8,7 +8,7 @@
#include <utility>

#include <fcntl.h>
#ifdef _MSC_VER
#ifdef _WIN32
#include <io.h>
#else
#include <sys/stat.h>
Expand Down Expand Up @@ -79,20 +79,30 @@ class ParallelFileReader : public Reader {
}

size_t tell() override {
#ifdef _WIN32
return _lseeki64(fd_, 0, SEEK_CUR);
#else
return lseek(fd_, 0, SEEK_CUR);
#endif
}

// Warning: do not use this function from multiple threads as
// it advances the file descriptor
void seek(int64_t off, std::ios_base::seekdir way = std::ios_base::beg)
override {
int origin;
if (way == std::ios_base::beg) {
lseek(fd_, off, SEEK_SET);
origin = SEEK_SET;
} else if (way == std::ios_base::end) {
lseek(fd_, off, SEEK_END);
origin = SEEK_END;
} else {
lseek(fd_, off, SEEK_CUR);
origin = SEEK_CUR;
}
#ifdef _WIN32
_lseeki64(fd_, off, origin);
#else
lseek(fd_, off, origin);
#endif
}

// Warning: do not use this function from multiple threads as
Expand Down Expand Up @@ -159,19 +169,29 @@ class FileWriter : public Writer {

size_t tell() override {
check_open();
#ifdef _WIN32
return _lseeki64(fd_, 0, SEEK_CUR);
#else
return lseek(fd_, 0, SEEK_CUR);
#endif
}

void seek(int64_t off, std::ios_base::seekdir way = std::ios_base::beg)
override {
check_open();
int origin;
if (way == std::ios_base::beg) {
lseek(fd_, off, SEEK_SET);
origin = SEEK_SET;
} else if (way == std::ios_base::end) {
lseek(fd_, off, SEEK_END);
origin = SEEK_END;
} else {
lseek(fd_, off, SEEK_CUR);
origin = SEEK_CUR;
}
#ifdef _WIN32
_lseeki64(fd_, off, origin);
#else
lseek(fd_, off, origin);
#endif
}

void write(const char* data, size_t n) override {
Expand Down