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qemu/host-utils: Add wrappers for carry builtins

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These builtins came in clang 3.8, but are not present in gcc through
version 11.  Even in clang the optimization is only ideal on x86_64,
but never worse than the hand-coding that we currently do.

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
This commit is contained in:
Richard Henderson 2020-11-13 03:22:23 +00:00
parent cec07c0b61
commit 1ec8070e58
1 changed files with 50 additions and 0 deletions
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50
include/qemu/host-utils.h
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@ -26,6 +26,7 @@
#ifndef HOST_UTILS_H
#define HOST_UTILS_H
#include "qemu/compiler.h"
#include "qemu/bswap.h"
#ifdef CONFIG_INT128
@ -581,6 +582,55 @@ static inline bool umul64_overflow(uint64_t x, uint64_t y, uint64_t *ret)
#endif
}
/**
* uadd64_carry - addition with carry-in and carry-out
* @x, @y: addends
* @pcarry: in-out carry value
*
* Computes @x + @y + *@pcarry, placing the carry-out back
* into *@pcarry and returning the 64-bit sum.
*/
static inline uint64_t uadd64_carry(uint64_t x, uint64_t y, bool *pcarry)
{
#if __has_builtin(__builtin_addcll)
unsigned long long c = *pcarry;
x = __builtin_addcll(x, y, c, &c);
*pcarry = c & 1;
return x;
#else
bool c = *pcarry;
/* This is clang's internal expansion of __builtin_addc. */
c = uadd64_overflow(x, c, &x);
c |= uadd64_overflow(x, y, &x);
*pcarry = c;
return x;
#endif
}
/**
* usub64_borrow - subtraction with borrow-in and borrow-out
* @x, @y: addends
* @pborrow: in-out borrow value
*
* Computes @x - @y - *@pborrow, placing the borrow-out back
* into *@pborrow and returning the 64-bit sum.
*/
static inline uint64_t usub64_borrow(uint64_t x, uint64_t y, bool *pborrow)
{
#if __has_builtin(__builtin_subcll)
unsigned long long b = *pborrow;
x = __builtin_subcll(x, y, b, &b);
*pborrow = b & 1;
return x;
#else
bool b = *pborrow;
b = usub64_overflow(x, b, &x);
b |= usub64_overflow(x, y, &x);
*pborrow = b;
return x;
#endif
}
/* Host type specific sizes of these routines. */
#if ULONG_MAX == UINT32_MAX