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c138e6a4b2
On x86-64 platforms, we can rely on BSR not changing the destination operand when the input is zero. Signed-off-by: H. Peter Anvin <hpa@zytor.com>
161 lines
3.6 KiB
C
161 lines
3.6 KiB
C
/* ----------------------------------------------------------------------- *
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*
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* Copyright 1996-2010 The NASM Authors - All Rights Reserved
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* See the file AUTHORS included with the NASM distribution for
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* the specific copyright holders.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following
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* conditions are met:
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*
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* * Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* * Redistributions in binary form must reproduce the above
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* copyright notice, this list of conditions and the following
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* disclaimer in the documentation and/or other materials provided
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* with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
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* CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
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* INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
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* MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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* DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
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* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
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* OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
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* EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*
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* ----------------------------------------------------------------------- */
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#include "compiler.h"
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#include "nasmlib.h"
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#define ROUND(v, a, w) \
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do { \
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if (v & (((1 << w) - 1) << w)) { \
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a += w; \
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v >>= w; \
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} \
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} while (0)
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#if defined(__GNUC__) && defined(__x86_64__)
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int ilog2_32(uint32_t v)
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{
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int n;
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__asm__("bsrl %1,%0"
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: "=r" (n)
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: "rm" (v), "0" (0));
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return n;
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}
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#elif defined(__GNUC__) && defined(__i386__)
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int ilog2_32(uint32_t v)
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{
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int n;
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__asm__("bsrl %1,%0 ; jnz 1f ; xorl %0,%0\n"
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"1:"
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: "=&r" (n)
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: "rm" (v));
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return n;
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}
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#elif defined(HAVE_GNUC_4)
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int ilog2_32(uint32_t v)
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{
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if (!v)
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return 0;
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return __builtin_clz(v) ^ 31;
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}
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#else
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int ilog2_32(uint32_t v)
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{
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int p = 0;
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ROUND(v, p, 16);
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ROUND(v, p, 8);
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ROUND(v, p, 4);
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ROUND(v, p, 2);
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ROUND(v, p, 1);
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return p;
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}
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#endif
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#if defined(__GNUC__) && defined(__x86_64__)
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int ilog2_64(uint64_t v)
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{
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uint64_t n;
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__asm__("bsrq %1,%0"
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: "=r" (n)
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: "rm" (v), "0" (UINT64_C(0)));
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return n;
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}
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#elif defined(HAVE_GNUC_4)
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int ilog2_64(uint64_t v)
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{
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if (!v)
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return 0;
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return __builtin_clzll(v) ^ 63;
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}
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#else
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int ilog2_64(uint64_t vv)
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{
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int p = 0;
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uint32_t v;
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v = vv >> 32;
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if (v)
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p += 32;
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else
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v = vv;
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ROUND(v, p, 16);
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ROUND(v, p, 8);
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ROUND(v, p, 4);
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ROUND(v, p, 2);
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ROUND(v, p, 1);
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return p;
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}
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#endif
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/*
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* v == 0 ? 0 : is_power2(x) ? ilog2_X(v) : -1
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*/
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int alignlog2_32(uint32_t v)
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{
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if (unlikely(v & (v-1)))
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return -1; /* invalid alignment */
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return ilog2_32(v);
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}
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int alignlog2_64(uint64_t v)
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{
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if (unlikely(v & (v-1)))
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return -1; /* invalid alignment */
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return ilog2_64(v);
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}
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