mirror of
https://github.com/CloverHackyColor/CloverBootloader.git
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65 lines
1.6 KiB
C
65 lines
1.6 KiB
C
/** @file
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Copyright (C) 2019, Download-Fritz. All rights reserved.
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This program and the accompanying materials
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are licensed and made available under the terms and conditions of the BSD License
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which accompanies this distribution. The full text of the license may be found at
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http://opensource.org/licenses/bsd-license.php
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THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
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WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
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**/
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#include <Base.h>
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#include <Library/DebugLib.h>
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#include <Library/OcGuardLib.h>
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#include "../BigNumLib.h"
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OC_BN_WORD
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BigNumWordMul64 (
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OUT OC_BN_WORD *Hi,
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IN OC_BN_WORD A,
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IN OC_BN_WORD B
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)
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{
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ASSERT (OC_BN_WORD_SIZE == sizeof (UINT64));
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ASSERT (Hi != NULL);
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//
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// This is to be used when the used compiler lacks support for both the
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// __int128 type and a suiting intrinsic to perform the calculation.
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//
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// Source: https://stackoverflow.com/a/31662911
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//
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CONST OC_BN_WORD SubWordShift = OC_BN_WORD_NUM_BITS / 2;
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CONST OC_BN_WORD SubWordMask = ((OC_BN_WORD)1U << SubWordShift) - 1;
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OC_BN_WORD ALo;
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OC_BN_WORD AHi;
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OC_BN_WORD BLo;
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OC_BN_WORD BHi;
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OC_BN_WORD P0;
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OC_BN_WORD P1;
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OC_BN_WORD P2;
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OC_BN_WORD P3;
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OC_BN_WORD Cy;
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ALo = A & SubWordMask;
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AHi = A >> SubWordShift;
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BLo = B & SubWordMask;
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BHi = B >> SubWordShift;
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P0 = ALo * BLo;
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P1 = ALo * BHi;
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P2 = AHi * BLo;
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P3 = AHi * BHi;
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Cy = (((P0 >> SubWordShift) + (P1 & SubWordMask) + (P2 & SubWordMask)) >> SubWordShift) & SubWordMask;
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*Hi = P3 + (P1 >> SubWordShift) + (P2 >> SubWordShift) + Cy;
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return P0 + (P1 << SubWordShift) + (P2 << SubWordShift);
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}
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