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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
// ----------------------------------------------------------------------------
// Optionally subtract, z := x - y (if p nonzero) or z := x (if p zero)
// Inputs x[k], p, y[k]; outputs function return (carry-out) and z[k]
//
// extern uint64_t bignum_optsub(uint64_t k, uint64_t *z, const uint64_t *x,
// uint64_t p, const uint64_t *y);
//
// It is assumed that all numbers x, y and z have the same size k digits.
// Returns carry-out as per usual subtraction, always 0 if p was zero.
//
// Standard ARM ABI: X0 = k, X1 = z, X2 = x, X3 = p, X4 = y, returns X0
// ----------------------------------------------------------------------------
macro_rules! k {
() => {
"x0"
};
}
macro_rules! z {
() => {
"x1"
};
}
macro_rules! x {
() => {
"x2"
};
}
macro_rules! p {
() => {
"x3"
};
}
macro_rules! m {
() => {
"x3"
};
}
macro_rules! y {
() => {
"x4"
};
}
macro_rules! a {
() => {
"x5"
};
}
macro_rules! b {
() => {
"x6"
};
}
macro_rules! i {
() => {
"x7"
};
}
/// Optionally subtract, z := x - y (if p nonzero) or z := x (if p zero)
///
/// Inputs x[k], p, y[k]; outputs function return (carry-out) and z[k]
///
/// It is assumed that all numbers x, y and z have the same size k digits.
/// Returns carry-out as per usual subtraction, always 0 if p was zero.
pub(crate) fn bignum_optsub(z: &mut [u64], x: &[u64], y: &[u64], p: u64) {
// SAFETY: inline assembly. see [crate::low::inline_assembly_safety] for safety info.
unsafe {
core::arch::asm!(
// if k = 0 do nothing. This is also the right top carry in X0
Q!(" cbz " k!() ", " Label!("bignum_optsub_end", 2, After)),
// Convert p into a strict bitmask (same register in fact)
Q!(" cmp " p!() ", xzr"),
Q!(" csetm " m!() ", ne"),
// Set i = 0 *and* make sure initial ~CF = 0
Q!(" subs " i!() ", xzr, xzr"),
// Main loop
Q!(Label!("bignum_optsub_loop", 3) ":"),
Q!(" ldr " a!() ", [" x!() ", " i!() "]"),
Q!(" ldr " b!() ", [" y!() ", " i!() "]"),
Q!(" and " b!() ", " b!() ", " m!()),
Q!(" sbcs " a!() ", " a!() ", " b!()),
Q!(" str " a!() ", [" z!() ", " i!() "]"),
Q!(" add " i!() ", " i!() ", #8"),
Q!(" sub " k!() ", " k!() ", #1"),
Q!(" cbnz " k!() ", " Label!("bignum_optsub_loop", 3, Before)),
// Return (non-inverted) carry flag
Q!(" cset " "x0, cc"),
Q!(Label!("bignum_optsub_end", 2) ":"),
inout("x0") z.len() => _,
inout("x1") z.as_mut_ptr() => _,
inout("x2") x.as_ptr() => _,
inout("x3") p => _,
inout("x4") y.as_ptr() => _,
// clobbers
out("x5") _,
out("x6") _,
out("x7") _,
)
};
}