| 1 | /*
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| 2 | * Copyright (c) 2009 Josef Cejka
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| 3 | * All rights reserved.
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| 4 | *
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| 5 | * Redistribution and use in source and binary forms, with or without
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| 6 | * modification, are permitted provided that the following conditions
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| 7 | * are met:
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| 8 | *
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| 9 | * - Redistributions of source code must retain the above copyright
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| 10 | * notice, this list of conditions and the following disclaimer.
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| 11 | * - Redistributions in binary form must reproduce the above copyright
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| 12 | * notice, this list of conditions and the following disclaimer in the
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| 13 | * documentation and/or other materials provided with the distribution.
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| 14 | * - The name of the author may not be used to endorse or promote products
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| 15 | * derived from this software without specific prior written permission.
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| 16 | *
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| 17 | * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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| 18 | * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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| 19 | * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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| 20 | * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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| 21 | * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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| 22 | * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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| 23 | * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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| 24 | * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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| 25 | * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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| 26 | * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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| 27 | */
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| 28 |
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| 29 | /** @addtogroup kernel_genarch
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| 30 | * @{
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| 31 | */
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| 32 | /**
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| 33 | * @file
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| 34 | * SW implementation of 32 and 64 bit multiplication.
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| 35 | */
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| 36 |
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| 37 | #include <genarch/softint/multiplication.h>
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| 38 |
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| 39 | /** Set 1 to return MAX_INT64 or MIN_INT64 on overflow */
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| 40 | #ifndef SOFTINT_CHECK_OF
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| 41 | # define SOFTINT_CHECK_OF 0
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| 42 | #endif
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| 43 |
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| 44 | #define MAX_UINT16 (0xFFFFu)
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| 45 | #define MAX_UINT32 (0xFFFFFFFFu)
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| 46 | #define MAX_INT64 (0x7FFFFFFFFFFFFFFFll)
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| 47 | #define MIN_INT64 (0x8000000000000000ll)
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| 48 |
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| 49 | /**
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| 50 | * Multiply two integers and return long long as result.
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| 51 | * This function is overflow safe.
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| 52 | * @param a
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| 53 | * @param b
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| 54 | * @result
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| 55 | */
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| 56 | static unsigned long long mul(unsigned int a, unsigned int b)
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| 57 | {
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| 58 | unsigned int a1, a2, b1, b2;
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| 59 | unsigned long long t1, t2, t3;
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| 60 |
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| 61 | a1 = a >> 16;
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| 62 | a2 = a & MAX_UINT16;
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| 63 | b1 = b >> 16;
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| 64 | b2 = b & MAX_UINT16;
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| 65 |
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| 66 | t1 = a1 * b1;
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| 67 | t2 = a1 * b2;
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| 68 | t2 += a2 * b1;
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| 69 | t3 = a2 * b2;
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| 70 |
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| 71 | t3 = (((t1 << 16) + t2) << 16) + t3;
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| 72 |
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| 73 | return t3;
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| 74 | }
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| 75 |
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| 76 | /** Emulate multiplication of two 64-bit long long integers.
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| 77 | *
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| 78 | */
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| 79 | long long __muldi3 (long long a, long long b)
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| 80 | {
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| 81 | long long result;
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| 82 | unsigned long long t1, t2;
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| 83 | unsigned long long a1, a2, b1, b2;
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| 84 | char neg = 0;
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| 85 |
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| 86 | if (a < 0) {
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| 87 | neg = !neg;
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| 88 | a = -a;
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| 89 | }
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| 90 |
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| 91 | if (b < 0) {
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| 92 | neg = !neg;
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| 93 | b = -b;
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| 94 | }
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| 95 |
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| 96 | a1 = a >> 32;
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| 97 | b1 = b >> 32;
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| 98 |
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| 99 | a2 = a & (MAX_UINT32);
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| 100 | b2 = b & (MAX_UINT32);
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| 101 |
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| 102 | if (SOFTINT_CHECK_OF && (a1 != 0) && (b1 != 0)) {
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| 103 | // error, overflow
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| 104 | return (neg ? MIN_INT64 : MAX_INT64);
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| 105 | }
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| 106 |
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| 107 | // (if OF checked) a1 or b1 is zero => result fits in 64 bits, no need to another overflow check
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| 108 | t1 = mul(a1, b2) + mul(b1, a2);
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| 109 |
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| 110 | if (SOFTINT_CHECK_OF && t1 > MAX_UINT32) {
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| 111 | // error, overflow
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| 112 | return (neg ? MIN_INT64 : MAX_INT64);
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| 113 | }
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| 114 |
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| 115 | t1 = t1 << 32;
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| 116 | t2 = mul(a2, b2);
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| 117 | t2 += t1;
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| 118 |
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| 119 | /*
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| 120 | * t2 & (1ull << 63) - if this bit is set in unsigned long long,
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| 121 | * result does not fit in signed one
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| 122 | */
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| 123 | if (SOFTINT_CHECK_OF && ((t2 < t1) || (t2 & (1ull << 63)))) {
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| 124 | // error, overflow
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| 125 | return (neg ? MIN_INT64 : MAX_INT64);
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| 126 | }
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| 127 |
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| 128 | result = t2;
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| 129 |
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| 130 | if (neg) {
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| 131 | result = -result;
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| 132 | }
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| 133 |
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| 134 | return result;
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| 135 | }
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| 136 |
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| 137 | /** @}
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| 138 | */
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