234 lines
7.4 KiB
C
234 lines
7.4 KiB
C
/*
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* Copyright 2014-2016 The OpenSSL Project Authors. All Rights Reserved.
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*
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* Licensed under the OpenSSL license (the "License"). You may not use
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* this file except in compliance with the License. You can obtain a copy
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* in the file LICENSE in the source distribution or at
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* https://www.openssl.org/source/license.html
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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 <stdlib.h>
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# include <openssl/e_os2.h> /* For 'ossl_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 ossl_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 ossl_inline unsigned int constant_time_lt(unsigned int a,
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unsigned int b);
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/* Convenience method for getting an 8-bit mask. */
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static ossl_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 ossl_inline unsigned int constant_time_ge(unsigned int a,
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unsigned int b);
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/* Convenience method for getting an 8-bit mask. */
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static ossl_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 ossl_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 ossl_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 ossl_inline unsigned int constant_time_eq(unsigned int a,
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unsigned int b);
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/* Convenience method for getting an 8-bit mask. */
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static ossl_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 ossl_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 ossl_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 ossl_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 ossl_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 ossl_inline int constant_time_select_int(unsigned int mask, int a,
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int b);
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static ossl_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 ossl_inline size_t constant_time_msb_s(size_t 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 ossl_inline unsigned int constant_time_lt(unsigned int a,
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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 ossl_inline size_t constant_time_lt_s(size_t a, size_t b)
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{
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return constant_time_msb_s(a ^ ((a ^ b) | ((a - b) ^ b)));
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}
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static ossl_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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return (unsigned char)(constant_time_lt(a, b));
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}
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static ossl_inline unsigned int constant_time_ge(unsigned int a,
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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 ossl_inline size_t constant_time_ge_s(size_t a, size_t b)
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{
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return ~constant_time_lt_s(a, b);
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}
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static ossl_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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return (unsigned char)(constant_time_ge(a, b));
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}
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static ossl_inline unsigned char constant_time_ge_8_s(size_t a, size_t b)
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{
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return (unsigned char)(constant_time_ge_s(a, b));
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}
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static ossl_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 ossl_inline size_t constant_time_is_zero_s(size_t a)
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{
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return constant_time_msb_s(~a & (a - 1));
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}
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static ossl_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 ossl_inline unsigned int constant_time_eq(unsigned int a,
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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 ossl_inline size_t constant_time_eq_s(size_t a, size_t b)
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{
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return constant_time_is_zero_s(a ^ b);
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}
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static ossl_inline unsigned char constant_time_eq_8(unsigned int a,
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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 ossl_inline unsigned char constant_time_eq_8_s(size_t a, size_t b)
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{
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return (unsigned char)(constant_time_eq_s(a, b));
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}
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static ossl_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 ossl_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 ossl_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 ossl_inline size_t constant_time_select_s(size_t mask,
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size_t a,
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size_t b)
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{
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return (mask & a) | (~mask & b);
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}
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static ossl_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 ossl_inline int constant_time_select_int(unsigned int mask, int a,
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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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static ossl_inline int constant_time_select_int_s(size_t mask, int a, int b)
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{
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return (int)(constant_time_select((unsigned)mask, (unsigned)(a),
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(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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