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Make CStr::from_ptr const.

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This commit is contained in:
Markus Reiter 2022-10-12 12:57:16 +02:00
parent e6ce5627a9
commit 328f81713c
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GPG Key ID: 245293B51702655B
1 changed files with 25 additions and 7 deletions
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32
library/core/src/ffi/c_str.rs
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@ -240,7 +240,9 @@ impl CStr {
#[inline]
#[must_use]
#[stable(feature = "rust1", since = "1.0.0")]
pub unsafe fn from_ptr<'a>(ptr: *const c_char) -> &'a CStr {
#[rustc_const_unstable(feature = "const_cstr_methods", issue = "101719")]
#[rustc_allow_const_fn_unstable(const_eval_select)]
pub const unsafe fn from_ptr<'a>(ptr: *const c_char) -> &'a CStr {
// SAFETY: The caller has provided a pointer that points to a valid C
// string with a NUL terminator of size less than `isize::MAX`, whose
// content remain valid and doesn't change for the lifetime of the
@ -252,13 +254,29 @@ impl CStr {
//
// The cast from c_char to u8 is ok because a c_char is always one byte.
unsafe {
extern "C" {
/// Provided by libc or compiler_builtins.
fn strlen(s: *const c_char) -> usize;
const fn strlen_ct(s: *const c_char) -> usize {
let mut len = 0;
// SAFETY: Outer caller has provided a pointer to a valid C string.
while unsafe { *s.add(len) } != 0 {
len += 1;
}
len
}
let len = strlen(ptr);
let ptr = ptr as *const u8;
CStr::from_bytes_with_nul_unchecked(slice::from_raw_parts(ptr, len as usize + 1))
fn strlen_rt(s: *const c_char) -> usize {
extern "C" {
/// Provided by libc or compiler_builtins.
fn strlen(s: *const c_char) -> usize;
}
// SAFETY: Outer caller has provided a pointer to a valid C string.
unsafe { strlen(s) }
}
let len = intrinsics::const_eval_select((ptr,), strlen_ct, strlen_rt);
Self::from_bytes_with_nul_unchecked(slice::from_raw_parts(ptr.cast(), len + 1))
}
}