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// generated source. do not edit.
#![allow(non_upper_case_globals, unused_macros, unused_imports)]
use crate::low::macros::*;
// Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
// SPDX-License-Identifier: Apache-2.0 OR ISC OR MIT-0
// ----------------------------------------------------------------------------
// Reduce modulo group order, z := x mod n_256
// Input x[4]; output z[4]
//
// extern void bignum_mod_n256_4(uint64_t z[static 4], const uint64_t x[static 4]);
//
// Reduction is modulo the group order of the NIST curve P-256.
//
// Standard x86-64 ABI: RDI = z, RSI = x
// Microsoft x64 ABI: RCX = z, RDX = x
// ----------------------------------------------------------------------------
macro_rules! z {
() => {
"rdi"
};
}
macro_rules! x {
() => {
"rsi"
};
}
macro_rules! d0 {
() => {
"rdx"
};
}
macro_rules! d1 {
() => {
"rcx"
};
}
macro_rules! d2 {
() => {
"r8"
};
}
macro_rules! d3 {
() => {
"r9"
};
}
macro_rules! n0 {
() => {
"rax"
};
}
macro_rules! n1 {
() => {
"r10"
};
}
macro_rules! n3 {
() => {
"r11"
};
}
macro_rules! n3short {
() => {
"r11d"
};
}
// Can re-use this as a temporary once we've loaded the input
macro_rules! c {
() => {
"rsi"
};
}
/// Reduce modulo group order, z := x mod n_256
///
/// Input x[4]; output z[4]
///
/// Reduction is modulo the group order of the NIST curve P-256.
pub(crate) fn bignum_mod_n256(z: &mut [u64; 4], x: &[u64; 4]) {
// SAFETY: inline assembly. see [crate::low::inline_assembly_safety] for safety info.
unsafe {
core::arch::asm!(
Q!(" endbr64 " ),
// Load a set of registers [n3; 0; n1; n0] = 2^256 - n_256
Q!(" mov " n0!() ", 0x0c46353d039cdaaf"),
Q!(" mov " n1!() ", 0x4319055258e8617b"),
Q!(" mov " n3short!() ", 0x00000000ffffffff"),
// Load the input and compute x + (2^256 - n_256)
Q!(" mov " d0!() ", [" x!() "]"),
Q!(" add " d0!() ", " n0!()),
Q!(" mov " d1!() ", [" x!() "+ 8]"),
Q!(" adc " d1!() ", " n1!()),
Q!(" mov " d2!() ", [" x!() "+ 16]"),
Q!(" adc " d2!() ", 0"),
Q!(" mov " d3!() ", [" x!() "+ 24]"),
Q!(" adc " d3!() ", " n3!()),
// Now CF is set iff 2^256 <= x + (2^256 - n_256), i.e. iff n_256 <= x.
// Create a mask for the condition x < n, and mask the three nontrivial digits
// ready to undo the previous addition with a compensating subtraction
Q!(" sbb " c!() ", " c!()),
Q!(" not " c!()),
Q!(" and " n0!() ", " c!()),
Q!(" and " n1!() ", " c!()),
Q!(" and " n3!() ", " c!()),
// Now subtract mask * (2^256 - n_256) again and store
Q!(" sub " d0!() ", " n0!()),
Q!(" mov " "[" z!() "], " d0!()),
Q!(" sbb " d1!() ", " n1!()),
Q!(" mov " "[" z!() "+ 8], " d1!()),
Q!(" sbb " d2!() ", 0"),
Q!(" mov " "[" z!() "+ 16], " d2!()),
Q!(" sbb " d3!() ", " n3!()),
Q!(" mov " "[" z!() "+ 24], " d3!()),
inout("rdi") z.as_mut_ptr() => _,
inout("rsi") x.as_ptr() => _,
// clobbers
out("r10") _,
out("r11") _,
out("r8") _,
out("r9") _,
out("rax") _,
out("rcx") _,
out("rdx") _,
)
};
}