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[libc] Fix constexpr add_with_carry/sub_with_borrow #154282

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Merged
merged 3 commits into from
Aug 20, 2025
Merged

[libc] Fix constexpr add_with_carry/sub_with_borrow #154282

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1e57b21
[libc] Fix add_with_carry constexpr
gchatelet Aug 19, 2025
b9ff9b1
Also fix sub_with_borrow.
gchatelet Aug 19, 2025
59ccbd4
Merge branch 'llvm:main' into fix_add_with_carry_constexp
gchatelet Aug 19, 2025
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6 changes: 3 additions & 3 deletions libc/src/__support/math_extras.h
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Original file line number Diff line number Diff line change
Expand Up @@ -66,15 +66,15 @@ template <typename T>

#define RETURN_IF(TYPE, BUILTIN) \
if constexpr (cpp::is_same_v<T, TYPE>) \
return BUILTIN(a, b, carry_in, carry_out);
return BUILTIN(a, b, carry_in, &carry_out);

// Returns the result of 'a + b' taking into account 'carry_in'.
// The carry out is stored in 'carry_out' it not 'nullptr', dropped otherwise.
// We keep the pass by pointer interface for consistency with the intrinsic.
template <typename T>
[[nodiscard]] LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_unsigned_v<T>, T>
add_with_carry(T a, T b, T carry_in, T &carry_out) {
if constexpr (!cpp::is_constant_evaluated()) {
if (!cpp::is_constant_evaluated()) {
#if __has_builtin(__builtin_addcb)
RETURN_IF(unsigned char, __builtin_addcb)
#elif __has_builtin(__builtin_addcs)
Expand All @@ -100,7 +100,7 @@ add_with_carry(T a, T b, T carry_in, T &carry_out) {
template <typename T>
[[nodiscard]] LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_unsigned_v<T>, T>
sub_with_borrow(T a, T b, T carry_in, T &carry_out) {
if constexpr (!cpp::is_constant_evaluated()) {
if (!cpp::is_constant_evaluated()) {
#if __has_builtin(__builtin_subcb)
RETURN_IF(unsigned char, __builtin_subcb)
#elif __has_builtin(__builtin_subcs)
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