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// $OpenBSD: bignum_mul_8_16.S,v 1.4 2025/08/12 10:23:40 jsing Exp $
//
// Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
//
// Permission to use, copy, modify, and/or distribute this software for any
// purpose with or without fee is hereby granted, provided that the above
// copyright notice and this permission notice appear in all copies.
//
// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
// WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
// MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
// ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
// WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
// ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
// OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
// ----------------------------------------------------------------------------
// Multiply z := x * y
// Inputs x[8], y[8]; output z[16]
//
// extern void bignum_mul_8_16(uint64_t z[static 16], const uint64_t x[static 8],
// const uint64_t y[static 8]);
//
// Standard x86-64 ABI: RDI = z, RSI = x, RDX = y
// Microsoft x64 ABI: RCX = z, RDX = x, R8 = y
// ----------------------------------------------------------------------------
#include "s2n_bignum_internal.h"
.intel_syntax noprefix
S2N_BN_SYM_VISIBILITY_DIRECTIVE(bignum_mul_8_16)
S2N_BN_SYM_PRIVACY_DIRECTIVE(bignum_mul_8_16)
.text
// These are actually right
#define z rdi
#define x rsi
// Copied in or set up
#define y rcx
// A zero register
#define zero rbp
#define zeroe ebp
// mulpadd i, j adds x[i] * rdx (now assumed = y[j]) into the window at i+j
.macro mulpadd arg1,arg2
mulx rbx, rax, [x+8*\arg1]
.if ((\arg1 + \arg2) % 8 == 0)
adcx r8, rax
adox r9, rbx
.elseif ((\arg1 + \arg2) % 8 == 1)
adcx r9, rax
adox r10, rbx
.elseif ((\arg1 + \arg2) % 8 == 2)
adcx r10, rax
adox r11, rbx
.elseif ((\arg1 + \arg2) % 8 == 3)
adcx r11, rax
adox r12, rbx
.elseif ((\arg1 + \arg2) % 8 == 4)
adcx r12, rax
adox r13, rbx
.elseif ((\arg1 + \arg2) % 8 == 5)
adcx r13, rax
adox r14, rbx
.elseif ((\arg1 + \arg2) % 8 == 6)
adcx r14, rax
adox r15, rbx
.elseif ((\arg1 + \arg2) % 8 == 7)
adcx r15, rax
adox r8, rbx
.endif
.endm
// mulpade i, j adds x[i] * rdx (now assumed = y[j]) into the window at i+j
// but re-creates the top word assuming nothing to add there
.macro mulpade arg1,arg2
.if ((\arg1 + \arg2) % 8 == 0)
mulx r9, rax, [x+8*\arg1]
adcx r8, rax
adox r9, zero
.elseif ((\arg1 + \arg2) % 8 == 1)
mulx r10, rax, [x+8*\arg1]
adcx r9, rax
adox r10, zero
.elseif ((\arg1 + \arg2) % 8 == 2)
mulx r11, rax, [x+8*\arg1]
adcx r10, rax
adox r11, zero
.elseif ((\arg1 + \arg2) % 8 == 3)
mulx r12, rax, [x+8*\arg1]
adcx r11, rax
adox r12, zero
.elseif ((\arg1 + \arg2) % 8 == 4)
mulx r13, rax, [x+8*\arg1]
adcx r12, rax
adox r13, zero
.elseif ((\arg1 + \arg2) % 8 == 5)
mulx r14, rax, [x+8*\arg1]
adcx r13, rax
adox r14, zero
.elseif ((\arg1 + \arg2) % 8 == 6)
mulx r15, rax, [x+8*\arg1]
adcx r14, rax
adox r15, zero
.elseif ((\arg1 + \arg2) % 8 == 7)
mulx r8, rax, [x+8*\arg1]
adcx r15, rax
adox r8, zero
.endif
.endm
// Add in the whole j'th row
.macro addrow arg1
mov rdx, [y+8*\arg1]
xor zeroe, zeroe
mulpadd 0, \arg1
.if (\arg1 % 8 == 0)
mov [z+8*\arg1],r8
.elseif (\arg1 % 8 == 1)
mov [z+8*\arg1],r9
.elseif (\arg1 % 8 == 2)
mov [z+8*\arg1],r10
.elseif (\arg1 % 8 == 3)
mov [z+8*\arg1],r11
.elseif (\arg1 % 8 == 4)
mov [z+8*\arg1],r12
.elseif (\arg1 % 8 == 5)
mov [z+8*\arg1],r13
.elseif (\arg1 % 8 == 6)
mov [z+8*\arg1],r14
.elseif (\arg1 % 8 == 7)
mov [z+8*\arg1],r15
.endif
mulpadd 1, \arg1
mulpadd 2, \arg1
mulpadd 3, \arg1
mulpadd 4, \arg1
mulpadd 5, \arg1
mulpadd 6, \arg1
mulpade 7, \arg1
.if (\arg1 % 8 == 0)
adc r8, zero
.elseif (\arg1 % 8 == 1)
adc r9, zero
.elseif (\arg1 % 8 == 2)
adc r10, zero
.elseif (\arg1 % 8 == 3)
adc r11, zero
.elseif (\arg1 % 8 == 4)
adc r12, zero
.elseif (\arg1 % 8 == 5)
adc r13, zero
.elseif (\arg1 % 8 == 6)
adc r14, zero
.elseif (\arg1 % 8 == 7)
adc r15, zero
.endif
.endm
S2N_BN_SYMBOL(bignum_mul_8_16):
_CET_ENDBR
#if WINDOWS_ABI
push rdi
push rsi
mov rdi, rcx
mov rsi, rdx
mov rdx, r8
#endif
// Save more registers to play with
push rbp
push rbx
push r12
push r13
push r14
push r15
// Copy y into a safe register to start with
mov y, rdx
// Zero a register, which also makes sure we don't get a fake carry-in
xor zeroe, zeroe
// Do the zeroth row, which is a bit different
// Write back the zero-zero product and then accumulate
// r8,r15,r14,r13,r12,r11,r10,r9 as y[0] * x from 1..8
mov rdx, [y]
mulx r9, r8, [x]
mov [z], r8
mulx r10, rbx, [x+8]
adc r9, rbx
mulx r11, rbx, [x+16]
adc r10, rbx
mulx r12, rbx, [x+24]
adc r11, rbx
mulx r13, rbx, [x+32]
adc r12, rbx
mulx r14, rbx, [x+40]
adc r13, rbx
mulx r15, rbx, [x+48]
adc r14, rbx
mulx r8, rbx, [x+56]
adc r15, rbx
adc r8, zero
// Now all the other rows in a uniform pattern
addrow 1
addrow 2
addrow 3
addrow 4
addrow 5
addrow 6
addrow 7
// Now write back the additional columns
mov [z+64], r8
mov [z+72], r9
mov [z+80], r10
mov [z+88], r11
mov [z+96], r12
mov [z+104], r13
mov [z+112], r14
mov [z+120], r15
// Real epilog
pop r15
pop r14
pop r13
pop r12
pop rbx
pop rbp
#if WINDOWS_ABI
pop rsi
pop rdi
#endif
ret
#if defined(__linux__) && defined(__ELF__)
.section .note.GNU-stack,"",%progbits
#endif
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