qat_constant_time.h

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/*
 * This file is based on modified code from OpenSSL.
 * This is needed because the constant time functions are not exported
 * from OpenSSL forcing engines to have their own copy of the
 * functionality.
 * The code based on OpenSSL code is subject to the following license:
 */

/*
 * Copyright 2014-2016 The OpenSSL Project Authors. All Rights Reserved.
 *
 * Licensed under the OpenSSL license (the "License").  You may not use
 * this file except in compliance with the License.  You can obtain a copy
 * in the file LICENSE in the source distribution or at
 * https://www.openssl.org/source/license.html
 */

/*****************************************************************************
 * @file qat_constant_time.h
 *
 * This file provides constant time functions
 *
 *****************************************************************************/

#ifndef QAT_CONST_TIME_H
# define QAT_CONST_TIME_H

#ifdef __cplusplus
extern "C" {
#endif

static inline unsigned int qat_constant_time_msb(unsigned int a)
{
    return 0 - (a >> (sizeof(a) * 8 - 1));
}

static inline unsigned int qat_constant_time_lt(unsigned int a,
                                                unsigned int b)
{
    return qat_constant_time_msb(a ^ ((a ^ b) | ((a - b) ^ b)));
}

static inline unsigned int qat_constant_time_ge(unsigned int a,
                                                unsigned int b)
{
    return ~qat_constant_time_lt(a, b);
}

static inline unsigned char qat_constant_time_ge_8(unsigned int a,
                                                   unsigned int b)
{
    return (unsigned char)(qat_constant_time_ge(a, b));
}

static inline unsigned int qat_constant_time_is_zero(unsigned int a)
{
    return qat_constant_time_msb(~a & (a - 1));
}

static inline unsigned int qat_constant_time_eq(unsigned int a,
                                                unsigned int b)
{
    return qat_constant_time_is_zero(a ^ b);
}

#ifdef __cplusplus
}
#endif

#endif                          /* QAT_CONST_TIME_H */