github.com/twelsh-aw/go/src@v0.0.0-20230516233729-a56fe86a7c81/crypto/internal/edwards25519/field/fe_arm64.s (about)

     1  // Copyright (c) 2020 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  // +build arm64,gc,!purego
     6  
     7  #include "textflag.h"
     8  
     9  // carryPropagate works exactly like carryPropagateGeneric and uses the
    10  // same AND, ADD, and LSR+MADD instructions emitted by the compiler, but
    11  // avoids loading R0-R4 twice and uses LDP and STP.
    12  //
    13  // See https://golang.org/issues/43145 for the main compiler issue.
    14  //
    15  // func carryPropagate(v *Element)
    16  TEXT ·carryPropagate(SB),NOFRAME|NOSPLIT,$0-8
    17  	MOVD v+0(FP), R20
    18  
    19  	LDP 0(R20), (R0, R1)
    20  	LDP 16(R20), (R2, R3)
    21  	MOVD 32(R20), R4
    22  
    23  	AND $0x7ffffffffffff, R0, R10
    24  	AND $0x7ffffffffffff, R1, R11
    25  	AND $0x7ffffffffffff, R2, R12
    26  	AND $0x7ffffffffffff, R3, R13
    27  	AND $0x7ffffffffffff, R4, R14
    28  
    29  	ADD R0>>51, R11, R11
    30  	ADD R1>>51, R12, R12
    31  	ADD R2>>51, R13, R13
    32  	ADD R3>>51, R14, R14
    33  	// R4>>51 * 19 + R10 -> R10
    34  	LSR $51, R4, R21
    35  	MOVD $19, R22
    36  	MADD R22, R10, R21, R10
    37  
    38  	STP (R10, R11), 0(R20)
    39  	STP (R12, R13), 16(R20)
    40  	MOVD R14, 32(R20)
    41  
    42  	RET