| 1 |
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| 2 | #ifndef _ASM_GENERIC_DIV64_H
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| 3 | #define _ASM_GENERIC_DIV64_H
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| 4 | |
| 5 | * Copyright (C) 2003 Bernardo Innocenti <[email protected]>
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| 6 | * Based on former asm-ppc/div64.h and asm-m68knommu/div64.h
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| 7 | *
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| 8 | * Optimization for constant divisors on 32-bit machines:
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| 9 | * Copyright (C) 2006-2015 Nicolas Pitre
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| 10 | *
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| 11 | * The semantics of do_div() is, in C++ notation, observing that the name
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| 12 | * is a function-like macro and the n parameter has the semantics of a C++
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| 13 | * reference:
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| 14 | *
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| 15 | * uint32_t do_div(uint64_t &n, uint32_t base)
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| 16 | * {
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| 17 | * uint32_t remainder = n % base;
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| 18 | * n = n / base;
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| 19 | * return remainder;
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| 20 | * }
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| 21 | *
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| 22 | * NOTE: macro parameter n is evaluated multiple times,
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| 23 | * beware of side effects!
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| 24 |
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| 25 |
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| 26 | #include <linux/types.h>
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| 27 | #include <linux/compiler.h>
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| 28 |
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| 29 | #if BITS_PER_LONG == 64
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| 30 |
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| 31 | |
| 32 | * do_div - returns 2 values: calculate remainder and update new dividend
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| 33 | * @n: uint64_t dividend (will be updated)
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| 34 | * @base: uint32_t divisor
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| 35 | *
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| 36 | * Summary:
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| 37 | * ``uint32_t remainder = n % base;``
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| 38 | * ``n = n / base;``
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| 39 | *
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| 40 | * Return: (uint32_t)remainder
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| 41 | *
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| 42 | * NOTE: macro parameter @n is evaluated multiple times,
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| 43 | * beware of side effects!
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| 44 |
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| 45 | # define do_div(n,base) ({ \
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| 46 | uint32_t __base = (base); \
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| 47 | uint32_t __rem; \
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| 48 | __rem = ((uint64_t)(n)) % __base; \
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| 49 | (n) = ((uint64_t)(n)) / __base; \
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| 50 | __rem; \
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| 51 | })
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| 52 |
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| 53 | #elif BITS_PER_LONG == 32
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| 54 |
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| 55 | #include <linux/log2.h>
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| 56 |
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| 57 | |
| 58 | * If the divisor happens to be constant, we determine the appropriate
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| 59 | * inverse at compile time to turn the division into a few inline
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| 60 | * multiplications which ought to be much faster.
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| 61 | *
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| 62 | * (It is unfortunate that gcc doesn't perform all this internally.)
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| 63 |
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| 64 |
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| 65 | #define __div64_const32(n, ___b) \
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| 66 | ({ \
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| 67 | |
| 68 | * Multiplication by reciprocal of b: n / b = n * (p / b) / p \
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| 69 | * \
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| 70 | * We rely on the fact that most of this code gets optimized \
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| 71 | * away at compile time due to constant propagation and only \
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| 72 | * a few multiplication instructions should remain. \
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| 73 | * Hence this monstrous macro (static inline doesn't always \
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| 74 | * do the trick here). \
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| 75 | \
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| 76 | uint64_t ___res, ___x, ___t, ___m, ___n = (n); \
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| 77 | uint32_t ___p; \
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| 78 | bool ___bias = false; \
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| 79 | \
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| 80 | \
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| 81 | ___p = 1 << ilog2(___b); \
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| 82 | \
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| 83 | \
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| 84 | ___m = (~0ULL / ___b) * ___p; \
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| 85 | ___m += (((~0ULL % ___b + 1) * ___p) + ___b - 1) / ___b; \
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| 86 | \
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| 87 | \
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| 88 | ___x = ~0ULL / ___b * ___b - 1; \
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| 89 | \
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| 90 | \
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| 91 | ___res = (___m & 0xffffffff) * (___x & 0xffffffff); \
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| 92 | ___t = (___m & 0xffffffff) * (___x >> 32) + (___res >> 32); \
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| 93 | ___res = (___m >> 32) * (___x >> 32) + (___t >> 32); \
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| 94 | ___t = (___m >> 32) * (___x & 0xffffffff) + (___t & 0xffffffff);\
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| 95 | ___res = (___res + (___t >> 32)) / ___p; \
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| 96 | \
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| 97 | \
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| 98 | if (___res != ___x / ___b) { \
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| 99 | |
| 100 | * We can't get away without a bias to compensate \
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| 101 | * for bit truncation errors. To avoid it we'd need an \
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| 102 | * additional bit to represent m which would overflow \
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| 103 | * a 64-bit variable. \
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| 104 | * \
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| 105 | * Instead we do m = p / b and n / b = (n * m + m) / p. \
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| 106 | \
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| 107 | ___bias = true; \
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| 108 | \
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| 109 | ___m = (~0ULL / ___b) * ___p; \
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| 110 | ___m += ((~0ULL % ___b + 1) * ___p) / ___b; \
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| 111 | } \
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| 112 | \
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| 113 | \
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| 114 | ___p /= (___m & -___m); \
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| 115 | ___m /= (___m & -___m); \
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| 116 | \
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| 117 | |
| 118 | * Perform (m_bias + m * n) / (1 << 64). \
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| 119 | * From now on there will be actual runtime code generated. \
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| 120 | \
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| 121 | ___res = __arch_xprod_64(___m, ___n, ___bias); \
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| 122 | \
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| 123 | ___res /= ___p; \
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| 124 | })
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| 125 |
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| 126 | #ifndef __arch_xprod_64
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| 127 | |
| 128 | * Default C implementation for __arch_xprod_64()
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| 129 | *
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| 130 | * Prototype: uint64_t __arch_xprod_64(const uint64_t m, uint64_t n, bool bias)
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| 131 | * Semantic: retval = ((bias ? m : 0) + m * n) >> 64
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| 132 | *
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| 133 | * The product is a 128-bit value, scaled down to 64 bits.
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| 134 | * Hoping for compile-time optimization of conditional code.
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| 135 | * Architectures may provide their own optimized assembly implementation.
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| 136 |
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| 137 | #ifdef CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE
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| 138 | static __always_inline
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| 139 | #else
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| 140 | static inline
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| 141 | #endif
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| 142 | uint64_t __arch_xprod_64(const uint64_t m, uint64_t n, bool bias)
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| 143 | {
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| 144 | uint32_t m_lo = m;
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| 145 | uint32_t m_hi = m >> 32;
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| 146 | uint32_t n_lo = n;
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| 147 | uint32_t n_hi = n >> 32;
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| 148 | uint64_t x, y;
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| 149 |
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| 150 |
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| 151 | bool no_ovf = __builtin_constant_p(m) &&
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| 152 | ((m >> 32) + (m & 0xffffffff) < 0x100000000);
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| 153 |
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| 154 | if (no_ovf) {
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| 155 | x = (uint64_t)m_lo * n_lo + (bias ? m : 0);
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| 156 | x >>= 32;
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| 157 | x += (uint64_t)m_lo * n_hi;
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| 158 | x += (uint64_t)m_hi * n_lo;
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| 159 | x >>= 32;
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| 160 | x += (uint64_t)m_hi * n_hi;
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| 161 | } else {
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| 162 | x = (uint64_t)m_lo * n_lo + (bias ? m_lo : 0);
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| 163 | y = (uint64_t)m_lo * n_hi + (uint32_t)(x >> 32) + (bias ? m_hi : 0);
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| 164 | x = (uint64_t)m_hi * n_hi + (uint32_t)(y >> 32);
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| 165 | y = (uint64_t)m_hi * n_lo + (uint32_t)y;
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| 166 | x += (uint32_t)(y >> 32);
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| 167 | }
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| 168 |
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| 169 | return x;
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| 170 | }
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| 171 | #endif
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| 172 |
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| 173 | #ifndef __div64_32
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| 174 | extern uint32_t __div64_32(uint64_t *dividend, uint32_t divisor);
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| 175 | #endif
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| 176 |
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| 177 | |
| 178 | * to check for type safety (n must be 64bit)
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| 179 |
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| 180 | # define do_div(n,base) ({ \
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| 181 | uint32_t __base = (base); \
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| 182 | uint32_t __rem; \
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| 183 | (void)(((typeof((n)) *)0) == ((uint64_t *)0)); \
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| 184 | if (__builtin_constant_p(__base) && \
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| 185 | is_power_of_2(__base)) { \
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| 186 | __rem = (n) & (__base - 1); \
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| 187 | (n) >>= ilog2(__base); \
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| 188 | } else if (__builtin_constant_p(__base) && \
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| 189 | __base != 0) { \
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| 190 | uint32_t __res_lo, __n_lo = (n); \
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| 191 | (n) = __div64_const32(n, __base); \
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| 192 | \
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| 193 | __res_lo = (n); \
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| 194 | __rem = __n_lo - __res_lo * __base; \
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| 195 | } else if (likely(((n) >> 32) == 0)) { \
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| 196 | __rem = (uint32_t)(n) % __base; \
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| 197 | (n) = (uint32_t)(n) / __base; \
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| 198 | } else { \
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| 199 | __rem = __div64_32(&(n), __base); \
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| 200 | } \
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| 201 | __rem; \
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| 202 | })
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| 203 |
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| 204 | #else
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| 205 |
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| 206 | # error do_div() does not yet support the C64
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| 207 |
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| 208 | #endif
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| 209 |
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| 210 | #endif
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