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// 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 by a single word, z := c * y
// Inputs c, y[n]; outputs function return (carry-out) and z[k]
//
// extern uint64_t bignum_cmul
// (uint64_t k, uint64_t *z, uint64_t c, uint64_t n, uint64_t *y);
//
// Does the "z := c * y" operation where y is n digits, result z is p.
// Truncates the result in general unless p >= n + 1.
//
// The return value is a high/carry word that is meaningful when p >= n as
// giving the high part of the result. Since this is always zero if p > n,
// it is mainly of interest in the special case p = n, i.e. where the source
// and destination have the same nominal size, when it gives the extra word
// of the full result.
//
// Standard x86-64 ABI: RDI = k, RSI = z, RDX = c, RCX = n, R8 = y, returns RAX
// Microsoft x64 ABI: RCX = k, RDX = z, R8 = c, R9 = n, [RSP+40] = y, returns RAX
// ----------------------------------------------------------------------------
#include "s2n_bignum_internal.h"
.intel_syntax noprefix
S2N_BN_SYM_VISIBILITY_DIRECTIVE(bignum_cmul)
S2N_BN_SYM_PRIVACY_DIRECTIVE(bignum_cmul)
.text
#define p rdi
#define z rsi
#define c r9
#define n rcx
#define x r8
#define i r10
#define h r11
S2N_BN_SYMBOL(bignum_cmul):
#if WINDOWS_ABI
push rdi
push rsi
mov rdi, rcx
mov rsi, rdx
mov rdx, r8
mov rcx, r9
mov r8, [rsp+56]
#endif
// First clamp the input size n := min(p,n) since we can never need to read
// past the p'th term of the input to generate p-digit output. Now we can
// assume that n <= p
cmp p, n
cmovc n, p
// Initialize current input/output pointer offset i and high part h.
// But then if n = 0 skip the multiplication and go to the tail part
xor h, h
xor i, i
test n, n
jz tail
// Move c into a safer register as multiplies overwrite rdx
mov c, rdx
// Initialization of the loop: [h,l] = c * x_0
mov rax, [x]
mul c
mov [z], rax
mov h, rdx
inc i
cmp i, n
jz tail
// Main loop doing the multiplications
loop:
mov rax, [x+8*i]
mul c
add rax, h
adc rdx, 0
mov [z+8*i], rax
mov h, rdx
inc i
cmp i, n
jc loop
// Add a tail when the destination is longer
tail:
cmp i, p
jnc end
mov [z+8*i], h
xor h, h
inc i
cmp i, p
jnc end
tloop:
mov [z+8*i], h
inc i
cmp i, p
jc tloop
// Return the high/carry word
end:
mov rax, h
#if WINDOWS_ABI
pop rsi
pop rdi
#endif
ret
#if defined(__linux__) && defined(__ELF__)
.section .note.GNU-stack,"",%progbits
#endif
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