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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
// ----------------------------------------------------------------------------
// Shift bignum right by c < 64 bits z := floor(x / 2^c)
// Inputs x[n], c; outputs function return (bits shifted out) and z[k]
//
// extern uint64_t bignum_shr_small(uint64_t k, uint64_t *z, uint64_t n,
// const uint64_t *x, uint64_t c);
//
// Does the "z := x >> c" operation where x is n digits, result z is p.
// The shift count c is masked to 6 bits so it actually uses c' = c mod 64.
// The return value is the inout mod 2^c'.
//
// Standard ARM ABI: X0 = k, X1 = z, X2 = n, X3 = x, X4 = c, returns X0
// ----------------------------------------------------------------------------
macro_rules! p {
() => {
"x0"
};
}
macro_rules! z {
() => {
"x1"
};
}
macro_rules! n {
() => {
"x2"
};
}
macro_rules! x {
() => {
"x3"
};
}
macro_rules! c {
() => {
"x4"
};
}
macro_rules! d {
() => {
"x5"
};
}
macro_rules! a {
() => {
"x6"
};
}
macro_rules! b {
() => {
"x7"
};
}
macro_rules! m {
() => {
"x8"
};
}
macro_rules! t {
() => {
"x9"
};
}
/// Shift bignum right by c < 64 bits z := floor(x / 2^c)
///
/// Inputs x[n], c; outputs function return (bits shifted out) and z[k]
///
/// Does the "z := x >> c" operation where x is n digits, result z is p.
/// The shift count c is masked to 6 bits so it actually uses c' = c mod 64.
/// The return value is the inout mod 2^c'.
pub(crate) fn bignum_shr_small(z: &mut [u64], x: &[u64], c: u8) {
// SAFETY: inline assembly. see [crate::low::inline_assembly_safety] for safety info.
unsafe {
core::arch::asm!(
// Set default carry-in word to 0
Q!(" mov " b!() ", xzr"),
// First, if p > n then pad output on the left with p-n zeros
Q!(" cmp " n!() ", " p!()),
Q!(" bcs " Label!("bignum_shr_small_nopad", 2, After)),
Q!(Label!("bignum_shr_small_padloop", 3) ":"),
Q!(" sub " p!() ", " p!() ", #1"),
Q!(" str " "xzr, [" z!() ", " p!() ", lsl #3]"),
Q!(" cmp " n!() ", " p!()),
Q!(" bcc " Label!("bignum_shr_small_padloop", 3, Before)),
// We now know that p <= n. If in fact p < n let carry word = x[p] instead of 0
Q!(Label!("bignum_shr_small_nopad", 2) ":"),
Q!(" beq " Label!("bignum_shr_small_shiftstart", 4, After)),
Q!(" ldr " b!() ", [" x!() ", " p!() ", lsl #3]"),
Q!(Label!("bignum_shr_small_shiftstart", 4) ":"),
// Set up negated version of the shift and shift b in preparation.
// Use a mask for nonzero shift to fake 64-bit left shift in zero case
Q!(" neg " d!() ", " c!()),
Q!(" lsl " b!() ", " b!() ", " d!()),
Q!(" ands " "xzr, " c!() ", #63"),
Q!(" csetm " m!() ", ne"),
Q!(" and " b!() ", " b!() ", " m!()),
// Now the main loop
Q!(" cbz " p!() ", " Label!("bignum_shr_small_end", 5, After)),
Q!(Label!("bignum_shr_small_loop", 6) ":"),
Q!(" sub " p!() ", " p!() ", #1"),
Q!(" ldr " t!() ", [" x!() ", " p!() ", lsl #3]"),
Q!(" lsr " a!() ", " t!() ", " c!()),
Q!(" orr " a!() ", " a!() ", " b!()),
Q!(" lsl " b!() ", " t!() ", " d!()),
Q!(" and " b!() ", " b!() ", " m!()),
Q!(" str " a!() ", [" z!() ", " p!() ", lsl #3]"),
Q!(" cbnz " p!() ", " Label!("bignum_shr_small_loop", 6, Before)),
// Return top word, shifted back to be a modulus
Q!(Label!("bignum_shr_small_end", 5) ":"),
Q!(" lsr " "x0, " b!() ", " d!()),
inout("x0") z.len() => _,
inout("x1") z.as_ptr() => _,
inout("x2") x.len() => _,
inout("x3") x.as_ptr() => _,
inout("x4") (c as u64) => _,
// clobbers
out("x5") _,
out("x6") _,
out("x7") _,
out("x8") _,
out("x9") _,
)
};
}