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Comment on the casts in the seek implementations on files #34916

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Merged
merged 1 commit into from
Aug 6, 2016
Merged

Comment on the casts in the seek implementations on files #34916

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10 changes: 6 additions & 4 deletions src/libstd/sys/unix/fs.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -27,7 +27,7 @@ use sys_common::{AsInner, FromInner};
#[cfg(any(target_os = "linux", target_os = "emscripten"))]
use libc::{stat64, fstat64, lstat64, off64_t, ftruncate64, lseek64, dirent64, readdir64_r, open64};
#[cfg(target_os = "android")]
use libc::{stat as stat64, fstat as fstat64, lstat as lstat64, off64_t, lseek64,
use libc::{stat as stat64, fstat as fstat64, lstat as lstat64, lseek64,
dirent as dirent64, open as open64};
#[cfg(not(any(target_os = "linux",
target_os = "emscripten",
Expand Down Expand Up @@ -485,9 +485,11 @@ impl File {

pub fn seek(&self, pos: SeekFrom) -> io::Result<u64> {
let (whence, pos) = match pos {
SeekFrom::Start(off) => (libc::SEEK_SET, off as off64_t),
SeekFrom::End(off) => (libc::SEEK_END, off as off64_t),
SeekFrom::Current(off) => (libc::SEEK_CUR, off as off64_t),
// Casting to `i64` is fine, too large values will end up as
// negative which will cause an error in `lseek64`.
SeekFrom::Start(off) => (libc::SEEK_SET, off as i64),
SeekFrom::End(off) => (libc::SEEK_END, off),
SeekFrom::Current(off) => (libc::SEEK_CUR, off),
};
let n = cvt(unsafe { lseek64(self.0.raw(), pos, whence) })?;
Ok(n as u64)
Expand Down
2 changes: 2 additions & 0 deletions src/libstd/sys/windows/fs.rs
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Expand Up @@ -324,6 +324,8 @@ impl File {

pub fn seek(&self, pos: SeekFrom) -> io::Result<u64> {
let (whence, pos) = match pos {
// Casting to `i64` is fine, `SetFilePointerEx` reinterprets this
// integer as `u64`.
SeekFrom::Start(n) => (c::FILE_BEGIN, n as i64),
SeekFrom::End(n) => (c::FILE_END, n),
SeekFrom::Current(n) => (c::FILE_CURRENT, n),
Expand Down