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