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isqrt: cite source and rename variables to match original C code

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This commit is contained in:
Federico Stra 2023-09-28 12:12:18 +02:00
parent c97ab23141
commit 51463175a4
1 changed files with 15 additions and 10 deletions
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25
library/core/src/num/uint_macros.rs
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@ -1998,21 +1998,26 @@ macro_rules! uint_impl {
return self;
}
let mut x = self;
let mut c = 0;
let mut d = 1 << (self.ilog2() & !1);
// The algorithm is based on the one presented in
// <https://en.wikipedia.org/wiki/Methods_of_computing_square_roots#Binary_numeral_system_(base_2)>
// which cites as source the following C code:
// <https://web.archive.org/web/20120306040058/http://medialab.freaknet.org/martin/src/sqrt/sqrt.c>.
while d != 0 {
if x >= c + d {
x -= c + d;
c = (c >> 1) + d;
let mut op = self;
let mut res = 0;
let mut one = 1 << (self.ilog2() & !1);
while one != 0 {
if op >= res + one {
op -= res + one;
res = (res >> 1) + one;
} else {
c >>= 1;
res >>= 1;
}
d >>= 2;
one >>= 2;
}
c
res
}
/// Performs Euclidean division.