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32 lines
979 B
C
32 lines
979 B
C
#ifndef COSMOPOLITAN_LIBC_BITS_MIDPOINT_H_
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#define COSMOPOLITAN_LIBC_BITS_MIDPOINT_H_
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#include "libc/assert.h"
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#if !(__ASSEMBLER__ + __LINKER__ + 0)
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#if defined(__GNUC__) && !defined(__STRICT_ANSI__) && defined(__x86__)
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/**
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* Computes `(a + b) / 2` assuming unsigned.
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*
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* This implementation is the fastest on AMD Zen architecture.
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*/
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#define _midpoint(a, b) \
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({ \
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typeof((a) + (b)) a_ = (a); \
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typeof(a_) b_ = (b); \
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assert(a_ >= 0); \
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assert(b_ >= 0); \
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asm("add\t%1,%0\n\t" \
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"rcr\t%0" \
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: "+r"(a_) \
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: "r"(b_)); \
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a_; \
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})
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#else
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/**
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* Computes `(a + b) / 2` assuming unsigned.
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*/
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#define _midpoint(a, b) (((a) & (b)) + ((a) ^ (b)) / 2)
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#endif /* __GNUC__ && !__STRICT_ANSI__ && x86 */
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#endif /* !(__ASSEMBLER__ + __LINKER__ + 0) */
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#endif /* COSMOPOLITAN_LIBC_BITS_MIDPOINT_H_ */
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