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45 lines
1.3 KiB
C
45 lines
1.3 KiB
C
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#ifndef COSMOPOLITAN_LIBC_BITS_LOCKCMPXCHG16B_INTERNAL_H_
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#define COSMOPOLITAN_LIBC_BITS_LOCKCMPXCHG16B_INTERNAL_H_
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#include "libc/bits/bits.h"
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#if !(__ASSEMBLER__ + __LINKER__ + 0)
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COSMOPOLITAN_C_START_
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/**
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* Compares and exchanges 128-bit value, i.e.
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*
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* if (*IfThing == *IsEqualToMe) {
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* *IfThing = ReplaceItWithMe;
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* return true;
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* } else {
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* *IsEqualToMe = *IfThing;
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* return false;
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* }
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*
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* @param IfThing should point to aligned memory
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* @param IsEqualToMe should point to in/out local variable
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* @param ReplaceItWithMe might become the new memory value
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* @return true if *IfThing was changed
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* @asyncsignalsafe
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* @threadsafe
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*/
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static inline bool _lockcmpxchg16b(uint128_t *IfThing, uint128_t *IsEqualToMe,
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uint128_t ReplaceItWithMe) {
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bool DidIt;
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uint64_t ax, bx, cx, dx;
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ax = *IsEqualToMe;
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dx = *IsEqualToMe >> 64;
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bx = ReplaceItWithMe;
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cx = ReplaceItWithMe >> 64;
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asm volatile(ZFLAG_ASM("lock cmpxchg16b\t%1")
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: ZFLAG_CONSTRAINT(DidIt), "+m"(*IfThing), "+a"(ax), "+d"(dx)
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: "b"(bx), "c"(cx));
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if (!DidIt) {
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*IsEqualToMe = ax | (uint128_t)dx << 64;
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}
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return DidIt;
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}
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COSMOPOLITAN_C_END_
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#endif /* !(__ASSEMBLER__ + __LINKER__ + 0) */
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#endif /* COSMOPOLITAN_LIBC_BITS_LOCKCMPXCHG16B_INTERNAL_H_ */
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