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 /* SPDX-License-Identifier: GPL-2.0 */ #ifndef _ASM_GENERIC_DIV64_H #define _ASM_GENERIC_DIV64_H /* * Copyright (C) 2003 Bernardo Innocenti * 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() are: * * 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 #include #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 /* * 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. And yet only if compiling * with a sufficiently recent gcc version to perform proper 64-bit constant * propagation. * * (It is unfortunate that gcc doesn't perform all this internally.) */ #ifndef __div64_const32_is_OK #define __div64_const32_is_OK (__GNUC__ >= 4) #endif #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, ___bias; \ \ /* 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)) >> 32; \ ___t = ___res += (___m & 0xffffffff) * (___x >> 32); \ ___res += (___x & 0xffffffff) * (___m >> 32); \ ___t = (___res < ___t) ? (1ULL << 32) : 0; \ ___res = (___res >> 32) + ___t; \ ___res += (___m >> 32) * (___x >> 32); \ ___res /= ___p; \ \ /* Now sanitize and optimize what we've got. */ \ if (~0ULL % (___b / (___b & -___b)) == 0) { \ /* special case, can be simplified to ... */ \ ___n /= (___b & -___b); \ ___m = ~0ULL / (___b / (___b & -___b)); \ ___p = 1; \ ___bias = 1; \ } else 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 = 1; \ /* Compute m = (p << 64) / b */ \ ___m = (~0ULL / ___b) * ___p; \ ___m += ((~0ULL % ___b + 1) * ___p) / ___b; \ } else { \ /* \ * Reduce m / p, and try to clear bit 31 of m when \ * possible, otherwise that'll need extra overflow \ * handling later. \ */ \ uint32_t ___bits = -(___m & -___m); \ ___bits |= ___m >> 32; \ ___bits = (~___bits) << 1; \ /* \ * If ___bits == 0 then setting bit 31 is unavoidable. \ * Simply apply the maximum possible reduction in that \ * case. Otherwise the MSB of ___bits indicates the \ * best reduction we should apply. \ */ \ if (!___bits) { \ ___p /= (___m & -___m); \ ___m /= (___m & -___m); \ } else { \ ___p >>= ilog2(___bits); \ ___m >>= ilog2(___bits); \ } \ /* No bias needed. */ \ ___bias = 0; \ } \ \ /* \ * Now we have a combination of 2 conditions: \ * \ * 1) whether or not we need to apply a bias, and \ * \ * 2) whether or not there might be an overflow in the cross \ * product determined by (___m & ((1 << 63) | (1 << 31))). \ * \ * Select the best way to do (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. * Assuming constant propagation to optimize away unused conditional code. * Architectures may provide their own optimized assembly implementation. */ static inline 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 res; uint32_t res_lo, res_hi, tmp; if (!bias) { res = ((uint64_t)m_lo * n_lo) >> 32; } else if (!(m & ((1ULL << 63) | (1ULL << 31)))) { /* there can't be any overflow here */ res = (m + (uint64_t)m_lo * n_lo) >> 32; } else { res = m + (uint64_t)m_lo * n_lo; res_lo = res >> 32; res_hi = (res_lo < m_hi); res = res_lo | ((uint64_t)res_hi << 32); } if (!(m & ((1ULL << 63) | (1ULL << 31)))) { /* there can't be any overflow here */ res += (uint64_t)m_lo * n_hi; res += (uint64_t)m_hi * n_lo; res >>= 32; } else { res += (uint64_t)m_lo * n_hi; tmp = res >> 32; res += (uint64_t)m_hi * n_lo; res_lo = res >> 32; res_hi = (res_lo < tmp); res = res_lo | ((uint64_t)res_hi << 32); } res += (uint64_t)m_hi * n_hi; return res; } #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 (__div64_const32_is_OK && \ __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 */