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Linux kernel mirror (for testing) git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
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C
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123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132133134135136137138139140141142143144145146147148149150151152153154155156157158159160161162163164165166167168169170171172173174175176177178179180181182183184185186187188189190191192193194195196197198199200201202203204205206207208209210211/* SPDX-License-Identifier: GPL-2.0 */#ifndef _ASM_GENERIC_DIV64_H#define _ASM_GENERIC_DIV64_H/* * Copyright (C) 2003 Bernardo Innocenti <bernie@develer.com> * Based on former asm-ppc/div64.h and asm-m68knommu/div64.h * * Optimization for constant divisors on 32-bit machines: * Copyright (C) 2006-2015 Nicolas Pitre * * The semantics of do_div() is, in C++ notation, observing that the name * is a function-like macro and the n parameter has the semantics of a C++ * reference: * * uint32_t do_div(uint64_t &n, uint32_t base) * { * uint32_t remainder = n % base; * n = n / base; * return remainder; * } * * NOTE: macro parameter n is evaluated multiple times, * beware of side effects! */
#include <linux/types.h>#include <linux/compiler.h>
#if BITS_PER_LONG == 64
/** * do_div - returns 2 values: calculate remainder and update new dividend * @n: uint64_t dividend (will be updated) * @base: uint32_t divisor * * Summary: * ``uint32_t remainder = n % base;`` * ``n = n / base;`` * * Return: (uint32_t)remainder * * NOTE: macro parameter @n is evaluated multiple times, * beware of side effects! */# define do_div(n,base) ({ \ uint32_t __base = (base); \ uint32_t __rem; \ __rem = ((uint64_t)(n)) % __base; \ (n) = ((uint64_t)(n)) / __base; \ __rem; \ })
#elif BITS_PER_LONG == 32
#include <linux/log2.h>
/* * If the divisor happens to be constant, we determine the appropriate * inverse at compile time to turn the division into a few inline * multiplications which ought to be much faster. * * (It is unfortunate that gcc doesn't perform all this internally.) */
#define __div64_const32(n, ___b) \({ \ /* \ * Multiplication by reciprocal of b: n / b = n * (p / b) / p \ * \ * We rely on the fact that most of this code gets optimized \ * away at compile time due to constant propagation and only \ * a few multiplication instructions should remain. \ * Hence this monstrous macro (static inline doesn't always \ * do the trick here). \ */ \ uint64_t ___res, ___x, ___t, ___m, ___n = (n); \ uint32_t ___p; \ bool ___bias = false; \ \ /* determine MSB of b */ \ ___p = 1 << ilog2(___b); \ \ /* compute m = ((p << 64) + b - 1) / b */ \ ___m = (~0ULL / ___b) * ___p; \ ___m += (((~0ULL % ___b + 1) * ___p) + ___b - 1) / ___b; \ \ /* one less than the dividend with highest result */ \ ___x = ~0ULL / ___b * ___b - 1; \ \ /* test our ___m with res = m * x / (p << 64) */ \ ___res = (___m & 0xffffffff) * (___x & 0xffffffff); \ ___t = (___m & 0xffffffff) * (___x >> 32) + (___res >> 32); \ ___res = (___m >> 32) * (___x >> 32) + (___t >> 32); \ ___t = (___m >> 32) * (___x & 0xffffffff) + (___t & 0xffffffff);\ ___res = (___res + (___t >> 32)) / ___p; \ \ /* Now validate what we've got. */ \ if (___res != ___x / ___b) { \ /* \ * We can't get away without a bias to compensate \ * for bit truncation errors. To avoid it we'd need an \ * additional bit to represent m which would overflow \ * a 64-bit variable. \ * \ * Instead we do m = p / b and n / b = (n * m + m) / p. \ */ \ ___bias = true; \ /* Compute m = (p << 64) / b */ \ ___m = (~0ULL / ___b) * ___p; \ ___m += ((~0ULL % ___b + 1) * ___p) / ___b; \ } \ \ /* Reduce m / p to help avoid overflow handling later. */ \ ___p /= (___m & -___m); \ ___m /= (___m & -___m); \ \ /* \ * Perform (m_bias + m * n) / (1 << 64). \ * From now on there will be actual runtime code generated. \ */ \ ___res = __arch_xprod_64(___m, ___n, ___bias); \ \ ___res /= ___p; \})
#ifndef __arch_xprod_64/* * Default C implementation for __arch_xprod_64() * * Prototype: uint64_t __arch_xprod_64(const uint64_t m, uint64_t n, bool bias) * Semantic: retval = ((bias ? m : 0) + m * n) >> 64 * * The product is a 128-bit value, scaled down to 64 bits. * Hoping for compile-time optimization of conditional code. * Architectures may provide their own optimized assembly implementation. */#ifdef CONFIG_CC_OPTIMIZE_FOR_PERFORMANCEstatic __always_inline#elsestatic inline#endifuint64_t __arch_xprod_64(const uint64_t m, uint64_t n, bool bias){ uint32_t m_lo = m; uint32_t m_hi = m >> 32; uint32_t n_lo = n; uint32_t n_hi = n >> 32; uint64_t x, y;
/* Determine if overflow handling can be dispensed with. */ bool no_ovf = __builtin_constant_p(m) && ((m >> 32) + (m & 0xffffffff) < 0x100000000);
if (no_ovf) { x = (uint64_t)m_lo * n_lo + (bias ? m : 0); x >>= 32; x += (uint64_t)m_lo * n_hi; x += (uint64_t)m_hi * n_lo; x >>= 32; x += (uint64_t)m_hi * n_hi; } else { x = (uint64_t)m_lo * n_lo + (bias ? m_lo : 0); y = (uint64_t)m_lo * n_hi + (uint32_t)(x >> 32) + (bias ? m_hi : 0); x = (uint64_t)m_hi * n_hi + (uint32_t)(y >> 32); y = (uint64_t)m_hi * n_lo + (uint32_t)y; x += (uint32_t)(y >> 32); }
return x;}#endif
#ifndef __div64_32extern uint32_t __div64_32(uint64_t *dividend, uint32_t divisor);#endif
/* The unnecessary pointer compare is there * to check for type safety (n must be 64bit) */# define do_div(n,base) ({ \ uint32_t __base = (base); \ uint32_t __rem; \ (void)(((typeof((n)) *)0) == ((uint64_t *)0)); \ if (__builtin_constant_p(__base) && \ is_power_of_2(__base)) { \ __rem = (n) & (__base - 1); \ (n) >>= ilog2(__base); \ } else if (__builtin_constant_p(__base) && \ __base != 0) { \ uint32_t __res_lo, __n_lo = (n); \ (n) = __div64_const32(n, __base); \ /* the remainder can be computed with 32-bit regs */ \ __res_lo = (n); \ __rem = __n_lo - __res_lo * __base; \ } else if (likely(((n) >> 32) == 0)) { \ __rem = (uint32_t)(n) % __base; \ (n) = (uint32_t)(n) / __base; \ } else { \ __rem = __div64_32(&(n), __base); \ } \ __rem; \ })
#else /* BITS_PER_LONG == ?? */
# error do_div() does not yet support the C64
#endif /* BITS_PER_LONG */
#endif /* _ASM_GENERIC_DIV64_H */