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/* crypto/constant_time_locl.h */ |
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/*- |
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* Utilities for constant-time cryptography. |
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* |
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* Author: Emilia Kasper (emilia@openssl.org) |
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* Based on previous work by Bodo Moeller, Emilia Kasper, Adam Langley |
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* (Google). |
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* ==================================================================== |
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* Copyright (c) 2014 The OpenSSL Project. All rights reserved. |
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* |
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* Redistribution and use in source and binary forms, with or without |
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* modification, are permitted provided that the following conditions |
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* are met: |
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* 1. Redistributions of source code must retain the copyright |
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* notice, this list of conditions and the following disclaimer. |
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* 2. Redistributions in binary form must reproduce the above copyright |
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* notice, this list of conditions and the following disclaimer in the |
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* documentation and/or other materials provided with the distribution. |
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* 3. All advertising materials mentioning features or use of this software |
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* must display the following acknowledgement: |
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* "This product includes cryptographic software written by |
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* Eric Young (eay@cryptsoft.com)" |
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* The word 'cryptographic' can be left out if the rouines from the library |
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* being used are not cryptographic related :-). |
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* 4. If you include any Windows specific code (or a derivative thereof) from |
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* the apps directory (application code) you must include an acknowledgement: |
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* "This product includes software written by Tim Hudson (tjh@cryptsoft.com)" |
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* |
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* THIS SOFTWARE IS PROVIDED BY ERIC YOUNG ``AS IS'' AND |
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE |
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE |
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* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE |
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL |
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS |
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) |
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT |
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY |
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF |
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* SUCH DAMAGE. |
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* |
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* The licence and distribution terms for any publically available version or |
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* derivative of this code cannot be changed. i.e. this code cannot simply be |
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* copied and put under another distribution licence |
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* [including the GNU Public Licence.] |
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*/ |
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#ifndef HEADER_CONSTANT_TIME_LOCL_H |
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# define HEADER_CONSTANT_TIME_LOCL_H |
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__BEGIN_HIDDEN_DECLS |
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/*- |
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* The boolean methods return a bitmask of all ones (0xff...f) for true |
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* and 0 for false. This is useful for choosing a value based on the result |
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* of a conditional in constant time. For example, |
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* |
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* if (a < b) { |
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* c = a; |
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* } else { |
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* c = b; |
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* } |
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* |
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* can be written as |
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* |
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* unsigned int lt = constant_time_lt(a, b); |
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* c = constant_time_select(lt, a, b); |
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*/ |
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/* |
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* Returns the given value with the MSB copied to all the other |
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* bits. Uses the fact that arithmetic shift shifts-in the sign bit. |
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* However, this is not ensured by the C standard so you may need to |
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* replace this with something else on odd CPUs. |
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*/ |
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static inline unsigned int constant_time_msb(unsigned int a); |
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/* |
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* Returns 0xff..f if a < b and 0 otherwise. |
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*/ |
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static inline unsigned int constant_time_lt(unsigned int a, unsigned int b); |
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/* Convenience method for getting an 8-bit mask. */ |
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static inline unsigned char constant_time_lt_8(unsigned int a, |
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unsigned int b); |
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/* |
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* Returns 0xff..f if a >= b and 0 otherwise. |
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*/ |
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static inline unsigned int constant_time_ge(unsigned int a, unsigned int b); |
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/* Convenience method for getting an 8-bit mask. */ |
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static inline unsigned char constant_time_ge_8(unsigned int a, |
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unsigned int b); |
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/* |
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* Returns 0xff..f if a == 0 and 0 otherwise. |
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*/ |
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static inline unsigned int constant_time_is_zero(unsigned int a); |
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/* Convenience method for getting an 8-bit mask. */ |
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static inline unsigned char constant_time_is_zero_8(unsigned int a); |
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/* |
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* Returns 0xff..f if a == b and 0 otherwise. |
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*/ |
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static inline unsigned int constant_time_eq(unsigned int a, unsigned int b); |
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/* Convenience method for getting an 8-bit mask. */ |
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static inline unsigned char constant_time_eq_8(unsigned int a, |
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unsigned int b); |
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/* Signed integers. */ |
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static inline unsigned int constant_time_eq_int(int a, int b); |
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/* Convenience method for getting an 8-bit mask. */ |
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static inline unsigned char constant_time_eq_int_8(int a, int b); |
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/*- |
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* Returns (mask & a) | (~mask & b). |
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* |
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* When |mask| is all 1s or all 0s (as returned by the methods above), |
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* the select methods return either |a| (if |mask| is nonzero) or |b| |
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* (if |mask| is zero). |
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*/ |
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static inline unsigned int constant_time_select(unsigned int mask, |
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unsigned int a, |
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unsigned int b); |
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/* Convenience method for unsigned chars. */ |
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static inline unsigned char constant_time_select_8(unsigned char mask, |
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unsigned char a, |
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unsigned char b); |
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/* Convenience method for signed integers. */ |
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static inline int constant_time_select_int(unsigned int mask, int a, int b); |
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static inline unsigned int constant_time_msb(unsigned int a) |
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{ |
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return 0 - (a >> (sizeof(a) * 8 - 1)); |
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} |
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static inline unsigned int constant_time_lt(unsigned int a, unsigned int b) |
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{ |
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return constant_time_msb(a ^ ((a ^ b) | ((a - b) ^ b))); |
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} |
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static inline unsigned char constant_time_lt_8(unsigned int a, unsigned int b) |
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{ |
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return (unsigned char)(constant_time_lt(a, b)); |
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} |
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static inline unsigned int constant_time_ge(unsigned int a, unsigned int b) |
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{ |
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return ~constant_time_lt(a, b); |
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} |
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static inline unsigned char constant_time_ge_8(unsigned int a, unsigned int b) |
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{ |
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return (unsigned char)(constant_time_ge(a, b)); |
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} |
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static inline unsigned int constant_time_is_zero(unsigned int a) |
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{ |
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return constant_time_msb(~a & (a - 1)); |
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} |
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static inline unsigned char constant_time_is_zero_8(unsigned int a) |
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{ |
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return (unsigned char)(constant_time_is_zero(a)); |
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} |
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static inline unsigned int constant_time_eq(unsigned int a, unsigned int b) |
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{ |
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return constant_time_is_zero(a ^ b); |
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} |
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static inline unsigned char constant_time_eq_8(unsigned int a, unsigned int b) |
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{ |
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return (unsigned char)(constant_time_eq(a, b)); |
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} |
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static inline unsigned int constant_time_eq_int(int a, int b) |
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{ |
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return constant_time_eq((unsigned)(a), (unsigned)(b)); |
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} |
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static inline unsigned char constant_time_eq_int_8(int a, int b) |
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{ |
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return constant_time_eq_8((unsigned)(a), (unsigned)(b)); |
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} |
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static inline unsigned int constant_time_select(unsigned int mask, |
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unsigned int a, |
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unsigned int b) |
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{ |
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return (mask & a) | (~mask & b); |
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} |
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static inline unsigned char constant_time_select_8(unsigned char mask, |
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unsigned char a, |
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unsigned char b) |
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{ |
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return (unsigned char)(constant_time_select(mask, a, b)); |
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} |
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static inline int constant_time_select_int(unsigned int mask, int a, int b) |
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{ |
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return (int)(constant_time_select(mask, (unsigned)(a), (unsigned)(b))); |
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} |
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__END_HIDDEN_DECLS |
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#endif /* HEADER_CONSTANT_TIME_LOCL_H */ |