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math.big: add shrink zeros to karatsuba and toom-cook (#24937)

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Mike 2025-07-20 20:47:17 +03:00 committed by GitHub
parent 987c211517
commit 46d4a6f8af
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2 changed files with 27 additions and 2 deletions
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5
vlib/math/big/big_test.v
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File diff suppressed because one or more lines are too long

24
vlib/math/big/special_array_ops.v
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@ -13,6 +13,17 @@ fn shrink_tail_zeros(mut a []u32) {
}
}
@[direct_array_access; inline]
fn (i &Integer) shrink_tail_zeros() {
mut alen := i.digits.len
for alen > 0 && i.digits[alen - 1] == 0 {
alen--
}
unsafe {
i.digits.len = alen
}
}
// suppose operand_a bigger than operand_b and both not null.
// Both quotient and remaider are already allocated but of length 0
// TODO: the manualfree tag here is a workaround for compilation with -autofree. Remove it, when the -autofree bug is fixed.
@ -108,8 +119,8 @@ fn karatsuba_multiply_digit_array(operand_a []u32, operand_b []u32, mut storage
// thanks to the base cases we can pass zero-length arrays to the mult func
half := imax(operand_a.len, operand_b.len) / 2
a_l := unsafe { operand_a[0..half] }
a_h := unsafe { operand_a[half..] }
mut a_l := unsafe { operand_a[0..half] }
mut a_h := unsafe { operand_a[half..] }
mut b_l := []u32{}
mut b_h := []u32{}
if half <= operand_b.len {
@ -119,6 +130,10 @@ fn karatsuba_multiply_digit_array(operand_a []u32, operand_b []u32, mut storage
b_l = unsafe { operand_b }
// b_h = []u32{}
}
shrink_tail_zeros(mut a_l)
shrink_tail_zeros(mut a_h)
shrink_tail_zeros(mut b_l)
shrink_tail_zeros(mut b_h)
// use storage for p_1 to avoid allocation and copy later
multiply_digit_array(a_h, b_h, mut storage)
@ -171,6 +186,7 @@ fn toom3_multiply_digit_array(operand_a []u32, operand_b []u32, mut storage []u3
1
}
}
a0.shrink_tail_zeros()
a1 := Integer{
digits: unsafe { operand_a[k..k2] }
signum: if operand_a[k..k2].all(it == 0) {
@ -179,6 +195,7 @@ fn toom3_multiply_digit_array(operand_a []u32, operand_b []u32, mut storage []u3
1
}
}
a1.shrink_tail_zeros()
a2 := Integer{
digits: unsafe { operand_a[k2..] }
signum: 1
@ -201,6 +218,7 @@ fn toom3_multiply_digit_array(operand_a []u32, operand_b []u32, mut storage []u3
signum: 1
}
}
b0.shrink_tail_zeros()
b1 = Integer{
digits: operand_b[k..]
signum: 1
@ -212,12 +230,14 @@ fn toom3_multiply_digit_array(operand_a []u32, operand_b []u32, mut storage []u3
signum: 1
}
}
b0.shrink_tail_zeros()
if !operand_b[k..k2].all(it == 0) {
b1 = Integer{
digits: operand_b[k..k2]
signum: 1
}
}
b1.shrink_tail_zeros()
b2 = Integer{
digits: operand_b[k2..]
signum: 1