211 lines
7.5 KiB
C
211 lines
7.5 KiB
C
/* 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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# include "e_os.h" /* For 'inline' */
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#ifdef __cplusplus
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extern "C" {
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#endif
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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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#ifdef __cplusplus
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}
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#endif
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#endif /* HEADER_CONSTANT_TIME_LOCL_H */
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