37 lines
705 B
C
37 lines
705 B
C
/* LibTomCrypt, modular cryptographic library -- Tom St Denis */
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/* SPDX-License-Identifier: Unlicense */
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/**
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@file ocb_ntz.c
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OCB implementation, internal function, by Tom St Denis
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*/
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#include "tomcrypt_private.h"
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#ifdef LTC_OCB_MODE
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/**
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Returns the number of leading zero bits [from lsb up]
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@param x The 32-bit value to observe
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@return The number of bits [from the lsb up] that are zero
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*/
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int ocb_ntz(unsigned long x)
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{
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#if defined(LTC_HAVE_CTZL_BUILTIN)
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if (x == 0)
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return sizeof(unsigned long) * CHAR_BIT;
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return __builtin_ctzl(x);
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#else
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int c;
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x &= 0xFFFFFFFFUL;
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c = 0;
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while ((x & 1) == 0) {
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++c;
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x >>= 1;
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}
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return c;
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#endif
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}
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#endif
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