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https://github.com/Ed94/Odin.git
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Jeroen van Rijn
47 lines
1.1 KiB
Odin
47 lines
1.1 KiB
Odin
package bigint
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/*
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Copyright 2021 Jeroen van Rijn <nom@duclavier.com>.
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Made available under Odin's BSD-2 license.
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A BigInt implementation in Odin.
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For the theoretical underpinnings, see Knuth's The Art of Computer Programming, Volume 2, section 4.3.
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The code started out as an idiomatic source port of libTomMath, which is in the public domain, with thanks.
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*/
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log_n :: proc(a: ^Int, base: int) -> (log: int, err: Error) {
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assert_initialized(a);
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if is_neg(a) || is_zero(a) || base < 2 || DIGIT(base) > _DIGIT_MAX {
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return -1, .Invalid_Input;
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}
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if is_power_of_two(base) {
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return _log_power_of_two(a, base), .OK;
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}
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// if (MP_HAS(S_MP_LOG_D) && (a->used == 1)) {
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// *c = s_mp_log_d((mp_digit)base, a->dp[0]);
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// return MP_OKAY;
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// }
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// if (MP_HAS(S_MP_LOG)) {
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// return s_mp_log(a, (mp_digit)base, c);
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// }
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return -1, .Unimplemented;
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}
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/*
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Returns the log2 of an `Int`, provided `base` is a power of two.
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Don't call it if it isn't.
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*/
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_log_power_of_two :: proc(a: ^Int, base: int) -> (log: int) {
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base := base;
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y: int;
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for y = 0; base & 1 == 0; {
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y += 1;
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base >>= 1;
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}
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return (count_bits(a) - 1) / y;
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}
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