| 1 | /*
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| 2 | * Copyright (c) 2015 Jiri Svoboda
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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 libc
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| 30 | * @{
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| 31 | */
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| 32 | /**
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| 33 | * @file Integer mathematical functions
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| 34 | */
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| 35 |
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| 36 | #include <errno.h>
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| 37 | #include <imath.h>
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| 38 | #include <stdbool.h>
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| 39 | #include <stdint.h>
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| 40 |
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| 41 | /** Compute integer power of 10, unsigned 64-bit result.
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| 42 | *
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| 43 | * Fast algorithm using binary digits of exp to compute 10^exp in
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| 44 | * time O(log exp).
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| 45 | *
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| 46 | * @param exp Exponent
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| 47 | * @param res Place to store result
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| 48 | * @return EOK on success, ERANGE if result does not fit into result type
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| 49 | */
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| 50 | errno_t ipow10_u64(unsigned exp, uint64_t *res)
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| 51 | {
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| 52 | uint64_t a;
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| 53 | uint64_t r;
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| 54 |
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| 55 | r = 1;
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| 56 | a = 10;
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| 57 | while (true) {
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| 58 | if ((exp & 1) != 0) {
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| 59 | if ((r * a) / a != r)
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| 60 | return ERANGE;
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| 61 | r = r * a;
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| 62 | }
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| 63 |
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| 64 | exp = exp >> 1;
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| 65 | if (exp == 0)
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| 66 | break;
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| 67 |
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| 68 | if ((a * a) / a != a)
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| 69 | return ERANGE;
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| 70 | a = a * a;
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| 71 | }
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| 72 |
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| 73 | *res = r;
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| 74 | return EOK;
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| 75 | }
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| 76 |
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| 77 | /** Compute integer base 10 logarithm, unsigned 64-bit argument.
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| 78 | *
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| 79 | * For integer v, compute floor(log_10 v). Fast algorithm computing
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| 80 | * the binary digits of the result r in time O(log r).
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| 81 | *
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| 82 | * @param v Value to compute logarithm from
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| 83 | * @return Logarithm value
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| 84 | */
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| 85 | unsigned ilog10_u64(uint64_t v)
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| 86 | {
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| 87 | unsigned b;
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| 88 | unsigned e;
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| 89 | uint64_t p10p2[6];
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| 90 | uint64_t a;
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| 91 | unsigned r;
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| 92 |
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| 93 | /* Determine largest b such that 10^2^b <= v */
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| 94 | b = 0;
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| 95 | e = 1;
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| 96 | a = 10;
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| 97 | p10p2[0] = a;
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| 98 |
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| 99 | while (v / a >= a) {
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| 100 | ++b;
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| 101 | a = a * a;
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| 102 | e = e + e;
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| 103 | p10p2[b] = a;
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| 104 | }
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| 105 |
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| 106 | /* Determine the binary digits of largest e such that 10^e <= v */
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| 107 | r = 0;
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| 108 | while (true) {
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| 109 | if (v >= p10p2[b]) {
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| 110 | v = v / p10p2[b];
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| 111 | r = r ^ (1 << b);
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| 112 | }
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| 113 |
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| 114 | if (b == 0)
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| 115 | break;
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| 116 | --b;
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| 117 | }
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| 118 |
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| 119 | return r;
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| 120 | }
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| 121 |
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| 122 | /** @}
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| 123 | */
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