math.big: remove Newton-raphson division, remove related tests (#25168)

Author: tankf33der

vlib/math/big/array_ops.v

@@ -239,15 +239,9 @@ fn divide_array_by_digit(operand_a []u64, divisor u64, mut quotient []u64, mut r
 	shrink_tail_zeros(mut remainder)
 }
 
-const newton_division_limit = 1_000_000
-
 @[inline]
 fn divide_array_by_array(operand_a []u64, operand_b []u64, mut quotient []u64, mut remainder []u64) {
-	if operand_a.len >= newton_division_limit {
-		newton_divide_array_by_array(operand_a, operand_b, mut quotient, mut remainder)
-	} else {
-		binary_divide_array_by_array(operand_a, operand_b, mut quotient, mut remainder)
-	}
+	binary_divide_array_by_array(operand_a, operand_b, mut quotient, mut remainder)
 }
 
 // Shifts the contents of the original array by the given amount of bits to the left.

vlib/math/big/special_array_ops.v

@@ -24,57 +24,6 @@ fn (i &Integer) shrink_tail_zeros() {
 	}
 }
 
-// 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.
-@[manualfree]
-fn newton_divide_array_by_array(operand_a []u64, operand_b []u64, mut quotient []u64, mut remainder []u64) {
-	// transform back to Integers (on the stack without allocation)
-	a := Integer{
-		signum: 1
-		digits: operand_a
-	}
-	b := Integer{
-		signum: 1
-		digits: operand_b
-	}
-
-	k := a.bit_len() + b.bit_len() // a*b < 2**k
-	mut x := integer_from_int(2) //  0 < x < 2**(k+1)/b  // initial guess for convergence
-	// https://en.wikipedia.org/wiki/Division_algorithm#Newton%E2%80%93Raphson_division
-	// use 48/17 - (32/17)*D (divisor)
-	// where D - Divisor B adjusted to fit 0.5-1 range by replacing the exponent field with 8'd126
-	// 0x0f0f0f0f0f0f0f0f * 0x11 == 0xffffffff_ffffffff = -1
-	// 0x0f0f0f0f0f0f0f0f = -1/17
-	initial_guess := (((integer_from_int(48) - (integer_from_int(32) * b)) * integer_from_i64(0x0f0f0f0f0f0f0f0f)).right_shift(64)).neg() // / 17 == 0x11
-	if initial_guess > zero_int {
-		x = initial_guess
-	}
-	mut lastx := integer_from_int(0)
-	pow2_k_plus_1 := pow2(k + 1) // outside of the loop to optimize allocatio
-	for lastx != x { // main loop
-		lastx = x
-		x = (x * (pow2_k_plus_1 - (x * b))).right_shift(u32(k))
-	}
-	if x * b < pow2(k) {
-		x.inc()
-	}
-	mut q := (a * x).right_shift(u32(k))
-	// possible adjustments. see literature
-	if q * b > a {
-		q.dec()
-	}
-	mut r := a - (q * b)
-	if r >= b {
-		q.inc()
-		r -= b
-	}
-	quotient = q.digits.clone()
-	remainder = r.digits.clone()
-
-	shrink_tail_zeros(mut remainder)
-}
-
 // debug_u64_str output a `[]u64`
 @[direct_array_access]
 fn debug_u64_str(a []u64) string {

vlib/math/big/special_array_ops_test.v

@@ -128,66 +128,3 @@ fn test_multiply_karatsuba_05() {
 	}
 	assert c == expected.digits
 }
-
-fn test_newton_divide_03() {
-	a := [u64(0), 4]
-	b := [u64(0), 1]
-	mut q := []u64{cap: a.len - b.len + 1}
-	mut r := []u64{cap: a.len}
-
-	newton_divide_array_by_array(a, b, mut q, mut r)
-	assert q == [u64(4)]
-	assert r == []u64{len: 0}
-}
-
-fn test_newton_divide_04() {
-	a := [u64(2), 4]
-	b := [u64(0), 1]
-	mut q := []u64{cap: a.len - b.len + 1}
-	mut r := []u64{cap: a.len}
-
-	newton_divide_array_by_array(a, b, mut q, mut r)
-	assert q == [u64(4)]
-	assert r == [u64(2)]
-}
-
-fn test_newton_divide_05() {
-	a := [u64(2), 4, 5]
-	b := [u64(0), 1]
-	mut q := []u64{cap: a.len - b.len + 1}
-	mut r := []u64{cap: a.len}
-
-	newton_divide_array_by_array(a, b, mut q, mut r)
-	assert q == [u64(4), 5]
-	assert r == [u64(2)]
-}
-
-fn test_newton_divide_06() {
-	a := [u64(2), 4, 5, 3]
-	b := [u64(0), 0x8000]
-	mut q := []u64{cap: a.len - b.len + 1}
-	mut r := []u64{cap: a.len}
-
-	newton_divide_array_by_array(a, b, mut q, mut r)
-	assert q == [u64(0xa000_0000_0000), 0x6000_0000_0000]
-	assert r == [u64(2), 4]
-}
-
-fn test_newton_divide_07() {
-	a := integer_from_string('52348074924977237255285644820010078601114587486470740900886892189662650320988400136613780986308710610258879824881256666730655821800564143426560480113864123642197317383052431412305975584645367703594190956925565749714310612399025459615546540332117815550470167143256687163102859337019449165214274088466835988832405507818643018779158891710706073875995722420460085757') or {
-		panic(err)
-	}
-	b := integer_from_string('977091076523237491790970633699383779582771973038531457285598238843271083830214915826312193418602834034688531898668229388286706296786321423078510899614439367') or {
-		panic(err)
-	}
-	mut q := []u64{cap: a.digits.len - b.digits.len + 1}
-	mut r := []u64{cap: a.digits.len}
-
-	newton_divide_array_by_array(a.digits, b.digits, mut q, mut r)
-	quotient := Integer{
-		signum: 1
-		digits: q
-	}
-	assert quotient.str() == '53575430359313366047421252453000090528070240585276680372187519418517552556246806124659918940784792906379733645877657341259357264284615702179922887873492874019672838874121154927105373025311855709389770910765'
-	assert r == [u64(2)]
-}