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Some architectures may want to override the default implementation at compile time to do things inline. For example, ARM uses a non-standard calling convention for better efficiency in this case. Signed-off-by: Nicolas Pitre <nico@linaro.org>
234 lines
6.9 KiB
C
234 lines
6.9 KiB
C
#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() are:
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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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# 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. And yet only if compiling
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* with a sufficiently recent gcc version to perform proper 64-bit constant
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* propagation.
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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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#ifndef __div64_const32_is_OK
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#define __div64_const32_is_OK (__GNUC__ >= 4)
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#endif
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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, ___bias; \
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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)) >> 32; \
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___t = ___res += (___m & 0xffffffff) * (___x >> 32); \
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___res += (___x & 0xffffffff) * (___m >> 32); \
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___t = (___res < ___t) ? (1ULL << 32) : 0; \
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___res = (___res >> 32) + ___t; \
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___res += (___m >> 32) * (___x >> 32); \
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___res /= ___p; \
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\
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/* Now sanitize and optimize what we've got. */ \
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if (~0ULL % (___b / (___b & -___b)) == 0) { \
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/* special case, can be simplified to ... */ \
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___n /= (___b & -___b); \
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___m = ~0ULL / (___b / (___b & -___b)); \
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___p = 1; \
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___bias = 1; \
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} else 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 = 1; \
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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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} else { \
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/* \
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* Reduce m / p, and try to clear bit 31 of m when \
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* possible, otherwise that'll need extra overflow \
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* handling later. \
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*/ \
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uint32_t ___bits = -(___m & -___m); \
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___bits |= ___m >> 32; \
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___bits = (~___bits) << 1; \
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/* \
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* If ___bits == 0 then setting bit 31 is unavoidable. \
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* Simply apply the maximum possible reduction in that \
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* case. Otherwise the MSB of ___bits indicates the \
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* best reduction we should apply. \
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*/ \
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if (!___bits) { \
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___p /= (___m & -___m); \
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___m /= (___m & -___m); \
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} else { \
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___p >>= ilog2(___bits); \
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___m >>= ilog2(___bits); \
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} \
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/* No bias needed. */ \
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___bias = 0; \
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} \
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\
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/* \
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* Now we have a combination of 2 conditions: \
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* \
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* 1) whether or not we need to apply a bias, and \
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* \
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* 2) whether or not there might be an overflow in the cross \
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* product determined by (___m & ((1 << 63) | (1 << 31))). \
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* \
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* Select the best way to do (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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* Assuming constant propagation to optimize away unused conditional code.
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* Architectures may provide their own optimized assembly implementation.
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*/
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static inline 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 res, tmp;
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if (!bias) {
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res = ((uint64_t)m_lo * n_lo) >> 32;
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} else if (!(m & ((1ULL << 63) | (1ULL << 31)))) {
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/* there can't be any overflow here */
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res = (m + (uint64_t)m_lo * n_lo) >> 32;
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} else {
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res = m + (uint64_t)m_lo * n_lo;
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tmp = (res < m) ? (1ULL << 32) : 0;
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res = (res >> 32) + tmp;
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}
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if (!(m & ((1ULL << 63) | (1ULL << 31)))) {
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/* there can't be any overflow here */
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res += (uint64_t)m_lo * n_hi;
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res += (uint64_t)m_hi * n_lo;
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res >>= 32;
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} else {
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tmp = res += (uint64_t)m_lo * n_hi;
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res += (uint64_t)m_hi * n_lo;
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tmp = (res < tmp) ? (1ULL << 32) : 0;
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res = (res >> 32) + tmp;
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}
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res += (uint64_t)m_hi * n_hi;
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return res;
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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 (__div64_const32_is_OK && \
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__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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__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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