//

// equal.c  Memory comparison routine that is safe against side channels.

//

// Copyright (c) Microsoft Corporation. Licensed under the MIT license.

//

#include "precomp.h"

BOOLEAN

SYMCRYPT_CALL

SymCryptEqual(  _In_reads_( cbBytes )  PCBYTE pbSrc1,

                _In_reads_( cbBytes )  PCBYTE pbSrc2,

                                       SIZE_T cbBytes )

{

    UINT32 neq = 0;

    BYTE b;

    volatile BYTE * p1 = (volatile BYTE *) pbSrc1;

    volatile BYTE * p2 = (volatile BYTE *) pbSrc2;

    //

    // We use forced-access memory reads to ensure that the compiler doesn't get

    // smart and implement an early-out solution.

    //

    while( cbBytes >= 4 )

    {

        neq |= SYMCRYPT_FORCE_READ32( (volatile UINT32 *) p1 ) ^ SYMCRYPT_FORCE_READ32( (volatile UINT32 *) p2 );

        p1 += 4;

        p2 += 4;

        cbBytes -= 4;

    }

    // We have to deal with the remaining bytes using a separate accumulator to work around an issue in the ARM64 compiler.

    if( cbBytes > 0 )

    {

        b = 0;

        while( cbBytes > 0 )

        {

            b |= SYMCRYPT_FORCE_READ8( p1 ) ^ SYMCRYPT_FORCE_READ8( p2 );

            p1++;

            p2++;

            cbBytes--;

        }

        neq |= b;

    }

    return neq == 0;

}