diff options
Diffstat (limited to 'include/asm-generic/div64.h')
| -rw-r--r-- | include/asm-generic/div64.h | 145 |
1 files changed, 51 insertions, 94 deletions
diff --git a/include/asm-generic/div64.h b/include/asm-generic/div64.h index a3b98c86f077..25e7b4b58dcf 100644 --- a/include/asm-generic/div64.h +++ b/include/asm-generic/div64.h @@ -8,12 +8,14 @@ * Optimization for constant divisors on 32-bit machines: * Copyright (C) 2006-2015 Nicolas Pitre * - * The semantics of do_div() are: + * 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 do_div(uint64_t &n, uint32_t base) * { - * uint32_t remainder = *n % base; - * *n = *n / base; + * uint32_t remainder = n % base; + * n = n / base; * return remainder; * } * @@ -55,17 +57,11 @@ /* * 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. + * multiplications which ought to be much faster. * * (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) \ ({ \ /* \ @@ -78,7 +74,8 @@ * do the trick here). \ */ \ uint64_t ___res, ___x, ___t, ___m, ___n = (n); \ - uint32_t ___p, ___bias; \ + uint32_t ___p; \ + bool ___bias = false; \ \ /* determine MSB of b */ \ ___p = 1 << ilog2(___b); \ @@ -91,22 +88,14 @@ ___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; \ + ___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 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) { \ + /* 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 \ @@ -115,45 +104,18 @@ * \ * Instead we do m = p / b and n / b = (n * m + m) / p. \ */ \ - ___bias = 1; \ + ___bias = true; \ /* 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; \ } \ \ + /* Reduce m / p to help avoid overflow handling later. */ \ + ___p /= (___m & -___m); \ + ___m /= (___m & -___m); \ + \ /* \ - * 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). \ + * Perform (m_bias + m * n) / (1 << 64). \ * From now on there will be actual runtime code generated. \ */ \ ___res = __arch_xprod_64(___m, ___n, ___bias); \ @@ -169,47 +131,42 @@ * 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. + * Hoping for compile-time optimization of 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) +#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 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; + 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 { - 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); + 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); } - 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; + return x; } #endif @@ -228,8 +185,7 @@ extern uint32_t __div64_32(uint64_t *dividend, uint32_t divisor); is_power_of_2(__base)) { \ __rem = (n) & (__base - 1); \ (n) >>= ilog2(__base); \ - } else if (__div64_const32_is_OK && \ - __builtin_constant_p(__base) && \ + } else if (__builtin_constant_p(__base) && \ __base != 0) { \ uint32_t __res_lo, __n_lo = (n); \ (n) = __div64_const32(n, __base); \ @@ -239,8 +195,9 @@ extern uint32_t __div64_32(uint64_t *dividend, uint32_t divisor); } else if (likely(((n) >> 32) == 0)) { \ __rem = (uint32_t)(n) % __base; \ (n) = (uint32_t)(n) / __base; \ - } else \ + } else { \ __rem = __div64_32(&(n), __base); \ + } \ __rem; \ }) |