math.big: fix 1/115792089237316195423570985008687907853269984665640564039457584007908834671663 leading to panic (fix #23771)

Author: spytheman

vlib/math/big/big_test.v

@@ -194,7 +194,7 @@ const sub_test_data = [
 	SubTest{ 2, 100, -98},
 	SubTest{ -100, -2, -98},
 	SubTest{ 100, -2, 102},
-	SubTest{ 2, -100, 102},	
+	SubTest{ 2, -100, 102},
 	//
 	SubTest{ 2, 3, -1 },
 	SubTest{ 3, 2, 1 },
@@ -218,10 +218,10 @@ struct MulTest {
 // vfmt off
 const mul_test_data = [
 	MulTest{ 2, 3, 6 },
-	MulTest{ -2, 0, 0}, 
-	MulTest{  2, 0, 0}, 
-	MulTest{ 0, -2, 0}, 
-	MulTest{ 0, -2, 0}, 
+	MulTest{ -2, 0, 0},
+	MulTest{  2, 0, 0},
+	MulTest{ 0, -2, 0},
+	MulTest{ 0, -2, 0},
 	MulTest{ -869, 789, -685641 },
 	MulTest{ 869, -789, -685641 },
 	MulTest{ -869, -789, 685641 },
@@ -264,6 +264,7 @@ const div_mod_test_data = [
 		'629648864382619361826',
 		'2724578611525334851445652767465274410979805962941953382558409365935061481311529445551691298696266856092833571769883246719',
 	},
+     DivModTest{'1', '115792089237316195423570985008687907853269984665640564039457584007908834671663', '0', '1'},
 ]
 // vfmt on
 

vlib/math/big/integer.v

@@ -144,7 +144,8 @@ pub fn integer_from_bytes(oinput []u8, config IntegerConfig) Integer {
 	}
 	input := oinput[first_non_zero_index..]
 	// pad input
-	mut padded_input := []u8{len: ((input.len + 3) & ~0x3) - input.len, cap: (input.len + 3) & ~0x3}
+	mut padded_input := []u8{len: int_max(0, ((input.len + 3) & ~0x3) - input.len), cap: (
+		input.len + 3) & ~0x3}
 	padded_input << input
 	mut digits := []u32{len: padded_input.len / 4}
 	// combine every 4 bytes into a u32 and insert into n.digits
@@ -421,7 +422,7 @@ fn (dividend Integer) div_mod_internal(divisor Integer) (Integer, Integer) {
 		}
 	}
 	// Division for positive integers
-	mut q := []u32{cap: dividend.digits.len - divisor.digits.len + 1}
+	mut q := []u32{cap: int_max(1, dividend.digits.len - divisor.digits.len + 1)}
 	mut r := []u32{cap: dividend.digits.len}
 	divide_digit_array(dividend.digits, divisor.digits, mut q, mut r)
 	quotient := Integer{