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/* SPDX-License-Identifier: BSD-2-Clause */
/* Copyright 1996-2025 The NASM Authors - All Rights Reserved */
/*
* ilog2_xx(x) = x ? floor(log_2(x)) : 0
*/
#ifndef NASM_ILOG2_H
#define NASM_ILOG2_H
#include "compiler.h"
#ifdef ILOG2_C /* For generating the out-of-line functions */
# undef extern_inline
# define extern_inline
# define inline_prototypes
#endif
#ifdef inline_prototypes
extern unsigned int const_func ilog2_32(uint32_t v);
extern unsigned int const_func ilog2_64(uint64_t v);
extern int const_func alignlog2_32(uint32_t v);
extern int const_func alignlog2_64(uint64_t v);
#endif
#ifdef extern_inline
# define ROUND(v, a, w) \
do { \
if (v & (((UINT32_C(1) << w) - 1) << w)) { \
a += w; \
v >>= w; \
} \
} while (0)
# define static_nz(x) (is_constant(x != 0) && (x != 0))
# define defang_zero(x) ((x) | !static_nz(x))
# if defined(HAVE_STDC_LEADING_ZEROS)
extern_inline unsigned int const_func ilog2_32(uint32_t v)
{
return stdc_leading_zeros(defang_zero(v)) ^ 31;
}
extern_inline unsigned int const_func ilog2_64(uint64_t v)
{
return stdc_leading_zeros(defang_zero(v)) ^ 63;
}
# else
# if defined(HAVE___BUILTIN_CLZ) && INT_MAX == 2147483647
extern_inline unsigned int const_func ilog2_32(uint32_t v)
{
return __builtin_clz(v|1) ^ 31;
}
# elif defined(__GNUC__) && (defined(__x86_64__) || defined(__i386__))
extern_inline unsigned int const_func ilog2_32(uint32_t v)
{
unsigned int n;
# ifdef __x86_64__
__asm__("bsrl %1,%0"
: "=r" (n)
: "rm" (v), "0" (0));
# else
__asm__("bsrl %1,%0"
: "=r" (n)
: "rm" (defang_zero(v)));
# endif
return n;
}
# elif defined(HAVE__BITSCANREVERSE)
extern_inline unsigned int const_func ilog2_32(uint32_t v)
{
unsigned long ix;
return _BitScanReverse(&ix, v) ? v : 0;
}
# else
extern_inline unsigned int const_func ilog2_32(uint32_t v)
{
unsigned int p = 0;
ROUND(v, p, 16);
ROUND(v, p, 8);
ROUND(v, p, 4);
ROUND(v, p, 2);
ROUND(v, p, 1);
return p;
}
# endif
# if defined(HAVE__BUILTIN_CLZLL) && LLONG_MAX == 9223372036854775807LL
extern_inline unsigned int const_func ilog2_64(uint64_t v)
{
return __builtin_clzll(defang_zero(v)) ^ 63;
}
# elif defined(__GNUC__) && defined(__x86_64__)
extern_inline unsigned int const_func ilog2_64(uint64_t v)
{
uint64_t n;
__asm__("bsrq %1,%0"
: "=r" (n)
: "rm" (v), "0" (UINT64_C(0)));
return n;
}
# elif defined(HAVE__BITSCANREVERSE64)
extern_inline unsigned int const_func ilog2_64(uint64_t v)
{
unsigned long ix;
return _BitScanReverse64(&ix, v) ? ix : 0;
}
# else
extern_inline unsigned int const_func ilog2_64(uint64_t vv)
{
unsigned int p = 0;
uint32_t v;
v = vv >> 32;
if (v)
p += 32;
else
v = vv;
return p + ilog2_32(v);
}
# endif
# endif
/*
* v == 0 ? 0 : is_power2(x) ? ilog2_X(v) : -1
*/
extern_inline int const_func alignlog2_32(uint32_t v)
{
if (unlikely(v & (v-1)))
return -1; /* invalid alignment */
return ilog2_32(v);
}
extern_inline int const_func alignlog2_64(uint64_t v)
{
if (unlikely(v & (v-1)))
return -1; /* invalid alignment */
return ilog2_64(v);
}
#undef ROUND
#endif /* extern_inline */
#endif /* ILOG2_H */
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