| 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 | /**
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| 30 | * @file
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| 31 | * SW implementation of 32 and 64 bit multiplication.
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| 32 | */
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| 33 |
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| 34 | #include <genarch/multiplication.h>
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| 35 | #include <stdint.h>
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| 36 |
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| 37 | /** Set 1 to return INT64_MAX or INT64_MIN on overflow */
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| 38 | #ifndef SOFTINT_CHECK_OF
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| 39 | #define SOFTINT_CHECK_OF 0
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| 40 | #endif
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| 41 |
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| 42 | /** Multiply two integers and return long long as result.
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| 43 | *
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| 44 | * This function is overflow safe.
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| 45 | *
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| 46 | */
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| 47 | static unsigned long long mul(unsigned int a, unsigned int b)
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| 48 | {
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| 49 | unsigned int a1 = a >> 16;
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| 50 | unsigned int a2 = a & UINT16_MAX;
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| 51 | unsigned int b1 = b >> 16;
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| 52 | unsigned int b2 = b & UINT16_MAX;
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| 53 |
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| 54 | unsigned long long t1 = a1 * b1;
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| 55 | unsigned long long t2 = a1 * b2;
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| 56 | t2 += a2 * b1;
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| 57 | unsigned long long t3 = a2 * b2;
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| 58 |
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| 59 | t3 = (((t1 << 16) + t2) << 16) + t3;
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| 60 |
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| 61 | return t3;
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| 62 | }
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| 63 |
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| 64 | /** Emulate multiplication of two 64-bit long long integers.
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| 65 | *
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| 66 | */
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| 67 | long long __muldi3 (long long a, long long b)
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| 68 | {
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| 69 | char neg = 0;
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| 70 |
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| 71 | if (a < 0) {
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| 72 | neg = !neg;
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| 73 | a = -a;
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| 74 | }
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| 75 |
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| 76 | if (b < 0) {
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| 77 | neg = !neg;
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| 78 | b = -b;
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| 79 | }
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| 80 |
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| 81 | unsigned long long a1 = a >> 32;
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| 82 | unsigned long long b1 = b >> 32;
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| 83 |
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| 84 | unsigned long long a2 = a & (UINT32_MAX);
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| 85 | unsigned long long b2 = b & (UINT32_MAX);
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| 86 |
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| 87 | if (SOFTINT_CHECK_OF && (a1 != 0) && (b1 != 0)) {
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| 88 | /* Error (overflow) */
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| 89 | return (neg ? INT64_MIN : INT64_MAX);
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| 90 | }
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| 91 |
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| 92 | /*
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| 93 | * (if OF checked) a1 or b1 is zero => result fits in 64 bits,
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| 94 | * no need to another overflow check
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| 95 | */
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| 96 | unsigned long long t1 = mul(a1, b2) + mul(b1, a2);
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| 97 |
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| 98 | if ((SOFTINT_CHECK_OF) && (t1 > UINT32_MAX)) {
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| 99 | /* Error (overflow) */
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| 100 | return (neg ? INT64_MIN : INT64_MAX);
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| 101 | }
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| 102 |
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| 103 | t1 = t1 << 32;
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| 104 | unsigned long long t2 = mul(a2, b2);
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| 105 | t2 += t1;
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| 106 |
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| 107 | /*
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| 108 | * t2 & (1ull << 63) - if this bit is set in unsigned long long,
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| 109 | * result does not fit in signed one
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| 110 | */
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| 111 | if ((SOFTINT_CHECK_OF) && ((t2 < t1) || (t2 & (1ull << 63)))) {
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| 112 | /* Error (overflow) */
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| 113 | return (neg ? INT64_MIN : INT64_MAX);
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| 114 | }
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| 115 |
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| 116 | long long result = t2;
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| 117 | if (neg)
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| 118 | result = -result;
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| 119 |
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| 120 | return result;
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| 121 | }
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| 122 |
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| 123 | /** @}
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| 124 | */
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