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87d7010495
This change helps spectre more intelligently plan execution, by working around false output dependencies, impacting ops like popcnt bsr and bsf
43 lines
1.8 KiB
C
43 lines
1.8 KiB
C
#ifndef COSMOPOLITAN_LIBC_NEXGEN32E_BSR_H_
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#define COSMOPOLITAN_LIBC_NEXGEN32E_BSR_H_
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#if !(__ASSEMBLER__ + __LINKER__ + 0)
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COSMOPOLITAN_C_START_
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/*
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* BIT SCANNING 101
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* ctz(𝑥) 31^clz(𝑥) clz(𝑥)
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* uint32 𝑥 bsf(𝑥) tzcnt(𝑥) ffs(𝑥) bsr(𝑥) lzcnt(𝑥)
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* 0x00000000 wut 32 0 wut 32
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* 0x00000001 0 0 1 0 31
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* 0x80000001 0 0 1 31 0
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* 0x80000000 31 31 32 31 0
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* 0x00000010 4 4 5 4 27
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* 0x08000010 4 4 5 27 4
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* 0x08000000 27 27 28 27 4
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* 0xffffffff 0 0 1 31 0
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*/
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int bsr(int);
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int bsrl(long);
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int bsrll(long long);
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int bsrmax(uintmax_t);
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#if defined(__GNUC__) && defined(__x86_64__) && !defined(__STRICT_ANSI__)
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#define bsr(u) \
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({ \
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unsigned BiTs; \
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asm("bsr\t%0,%0" : "=r"(BiTs) : "0"((unsigned)(u)) : "cc"); \
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BiTs; \
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})
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#define bsrl(u) \
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({ \
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unsigned long BiTs; \
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asm("bsr\t%0,%0" : "=r"(BiTs) : "0"((unsigned long)(u)) : "cc"); \
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(unsigned)BiTs; \
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})
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#define bsrll(u) bsrl(u)
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#endif
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COSMOPOLITAN_C_END_
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#endif /* !(__ASSEMBLER__ + __LINKER__ + 0) */
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#endif /* COSMOPOLITAN_LIBC_NEXGEN32E_BSR_H_ */
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