math.big: change the return value of divmod to (quotient, remainder) (#10993)

vlib/math/big/big.v

@@ -135,9 +135,10 @@ pub fn (n &Number) str() string {
 	}
 	mut digits := []byte{}
 	mut x := n.clone()
-	div := Number{}
+
 	for !x.is_zero() {
-		mod := divmod(&x, &big.ten, &div)
+		// changes to reflect new api
+		div, mod := divmod(&x, &big.ten)
 		digits << byte(mod.int()) + `0`
 		x = div
 	}
@@ -192,10 +193,13 @@ pub fn (a &Number) % (b &Number) Number {
 	return c
 }
 
-pub fn divmod(a &Number, b &Number, c &Number) Number {
+// divmod returns a pair of quotient and remainder from div modulo operation
+// between two bignums `a` and `b`
+pub fn divmod(a &Number, b &Number) (Number, Number) {
+	c := Number{}
 	d := Number{}
-	C.bignum_divmod(a, b, c, &d)
-	return d
+	C.bignum_divmod(a, b, &c, &d)
+	return c, d
 }
 
 // //////////////////////////////////////////////////////////

vlib/math/big/big_test.v

@@ -90,6 +90,18 @@ fn test_mod() {
 	assert (big.from_u64(7) % big.from_u64(5)).int() == 2
 }
 
+fn test_divmod() {
+	x, y := big.divmod(big.from_u64(13), big.from_u64(10))
+	assert x.int() == 1
+	assert y.int() == 3
+	p, q := big.divmod(big.from_u64(13), big.from_u64(9))
+	assert p.int() == 1
+	assert q.int() == 4
+	c, d := big.divmod(big.from_u64(7), big.from_u64(5))
+	assert c.int() == 1
+	assert d.int() == 2
+}
+
 fn test_from_str() {
 	assert big.from_string('9870123').str() == '9870123'
 	assert big.from_string('').str() == '0'