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|
/// Implement field element inversion.
macro_rules! impl_field_invert {
(
$a:expr,
$one:expr,
$word_bits:expr,
$nlimbs:expr,
$mul:ident,
$neg:ident,
$divstep_precomp:ident,
$divstep:ident,
$msat:ident,
$selectznz:ident,
) => {{
const ITERATIONS: usize = (49 * $nlimbs * $word_bits + 57) / 17;
let mut d = 1;
let mut f = $msat();
let mut g = [0; $nlimbs + 1];
let mut v = [0; $nlimbs];
let mut r = $one;
let mut i = 0;
let mut j = 0;
while j < $nlimbs {
g[j] = $a[j];
j += 1;
}
while i < ITERATIONS - ITERATIONS % 2 {
let (out1, out2, out3, out4, out5) = $divstep(d, &f, &g, &v, &r);
let (out1, out2, out3, out4, out5) = $divstep(out1, &out2, &out3, &out4, &out5);
d = out1;
f = out2;
g = out3;
v = out4;
r = out5;
i += 2;
}
if ITERATIONS % 2 != 0 {
let (_out1, out2, _out3, out4, _out5) = $divstep(d, &f, &g, &v, &r);
v = out4;
f = out2;
}
let s = ((f[f.len() - 1] >> $word_bits - 1) & 1) as u8;
let v = $selectznz(s, &v, &$neg(&v));
$mul(&v, &$divstep_precomp())
}};
}
|
