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Diffstat (limited to 'include/asm-generic/div64.h')
| -rw-r--r-- | include/asm-generic/div64.h | 210 |
1 files changed, 210 insertions, 0 deletions
diff --git a/include/asm-generic/div64.h b/include/asm-generic/div64.h new file mode 100644 index 000000000..25e7b4b58 --- /dev/null +++ b/include/asm-generic/div64.h @@ -0,0 +1,210 @@ +/* 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_PERFORMANCE +static __always_inline +#else +static inline +#endif +uint64_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_32 +extern 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 */ |