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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
// ----------------------------------------------------------------------------
// Negate modulo p_256, z := (-x) mod p_256, assuming x reduced
// Input x[4]; output z[4]
//
// extern void bignum_neg_p256(uint64_t z[static 4], const uint64_t x[static 4]);
//
// Standard ARM ABI: X0 = z, X1 = x
// ----------------------------------------------------------------------------
macro_rules! z {
() => {
"x0"
};
}
macro_rules! x {
() => {
"x1"
};
}
macro_rules! p {
() => {
"x2"
};
}
macro_rules! t {
() => {
"x3"
};
}
macro_rules! d0 {
() => {
"x4"
};
}
macro_rules! d1 {
() => {
"x5"
};
}
macro_rules! d2 {
() => {
"x6"
};
}
macro_rules! d3 {
() => {
"x7"
};
}
/// Negate modulo p_256, z := (-x) mod p_256, assuming x reduced
///
/// Input x[4]; output z[4]
pub(crate) fn bignum_neg_p256(z: &mut [u64; 4], x: &[u64; 4]) {
// SAFETY: inline assembly. see [crate::low::inline_assembly_safety] for safety info.
unsafe {
core::arch::asm!(
// Load the 4 digits of x
Q!(" ldp " d0!() ", " d1!() ", [" x!() "]"),
Q!(" ldp " d2!() ", " d3!() ", [" x!() ", #16]"),
// Set a bitmask p for the input being nonzero, so that we avoid doing
// -0 = p_256 and hence maintain strict modular reduction
Q!(" orr " t!() ", " d0!() ", " d1!()),
Q!(" orr " p!() ", " d2!() ", " d3!()),
Q!(" orr " p!() ", " p!() ", " t!()),
Q!(" cmp " p!() ", #0"),
Q!(" csetm " p!() ", ne"),
// Mask the nontrivial words of p_256 = [n3;0;n1;-1] and subtract
Q!(" subs " d0!() ", " p!() ", " d0!()),
Q!(" and " t!() ", " p!() ", #0x00000000ffffffff"),
Q!(" sbcs " d1!() ", " t!() ", " d1!()),
Q!(" sbcs " d2!() ", xzr, " d2!()),
Q!(" and " t!() ", " p!() ", #0xffffffff00000001"),
Q!(" sbc " d3!() ", " t!() ", " d3!()),
// Write back the result
Q!(" stp " d0!() ", " d1!() ", [" z!() "]"),
Q!(" stp " d2!() ", " d3!() ", [" z!() ", #16]"),
// Return
inout("x0") z.as_mut_ptr() => _,
inout("x1") x.as_ptr() => _,
// clobbers
out("x2") _,
out("x3") _,
out("x4") _,
out("x5") _,
out("x6") _,
out("x7") _,
)
};
}