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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 x86-64 ABI: RDI = k, RSI = z, RDX = x, RCX = p, R8 = y, returns RAX
// Microsoft x64 ABI: RCX = k, RDX = z, R8 = x, R9 = p, [RSP+40] = y, returns RAX
// ----------------------------------------------------------------------------
macro_rules! k {
() => {
"rdi"
};
}
macro_rules! z {
() => {
"rsi"
};
}
macro_rules! x {
() => {
"rdx"
};
}
macro_rules! p {
() => {
"rcx"
};
}
macro_rules! y {
() => {
"r8"
};
}
macro_rules! i {
() => {
"r9"
};
}
macro_rules! b {
() => {
"r10"
};
}
macro_rules! c {
() => {
"rax"
};
}
macro_rules! a {
() => {
"r11"
};
}
/// 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!(
Q!(" endbr64 " ),
// Initialize top carry to zero in all cases (also return value)
Q!(" xor " c!() ", " c!()),
// If k = 0 do nothing
Q!(" test " k!() ", " k!()),
Q!(" jz " Label!("bignum_optsub_end", 2, After)),
// Convert the nonzero/zero status of p into an all-1s or all-0s mask
Q!(" neg " p!()),
Q!(" sbb " p!() ", " p!()),
// Now go round the loop for i=0...k-1, saving the carry in c each iteration
Q!(" xor " i!() ", " i!()),
Q!(Label!("bignum_optsub_loop", 3) ":"),
Q!(" mov " a!() ", [" x!() "+ 8 * " i!() "]"),
Q!(" mov " b!() ", [" y!() "+ 8 * " i!() "]"),
Q!(" and " b!() ", " p!()),
Q!(" neg " c!()),
Q!(" sbb " a!() ", " b!()),
Q!(" sbb " c!() ", " c!()),
Q!(" mov " "[" z!() "+ 8 * " i!() "], " a!()),
Q!(" inc " i!()),
Q!(" cmp " i!() ", " k!()),
Q!(" jc " Label!("bignum_optsub_loop", 3, Before)),
// Return top carry
Q!(" neg " "rax"),
Q!(Label!("bignum_optsub_end", 2) ":"),
inout("rdi") z.len() => _,
inout("rsi") z.as_mut_ptr() => _,
inout("rdx") x.as_ptr() => _,
inout("rcx") p => _,
inout("r8") y.as_ptr() => _,
// clobbers
out("r10") _,
out("r11") _,
out("r9") _,
out("rax") _,
)
};
}