math.big: add isqrt_checked and standardize error format

vlib/math/big/division_array_ops_test.v

@@ -146,6 +146,6 @@ fn random_number(length int) Integer {
 		nr := numbers[i]
 		stri = stri + nr.ascii_str()
 	}
-	res := integer_from_string(stri) or { panic('error in random_number') }
+	res := integer_from_string(stri) or { panic(err) }
 	return res
 }

vlib/math/big/integer.v

@@ -158,7 +158,7 @@ pub fn integer_from_string(characters string) !Integer {
 // integer_from_radix creates a new `big.Integer` from the given string and radix.
 pub fn integer_from_radix(all_characters string, radix u32) !Integer {
 	if radix < 2 || radix > 36 {
-		return error('Radix must be between 2 and 36 (inclusive)')
+		return error('math.big: Radix must be between 2 and 36 (inclusive)')
 	}
 	characters := all_characters.to_lower()
 	validate_string(characters, radix)!
@@ -186,10 +186,10 @@ fn validate_string(characters string, radix u32) ! {
 		value := big.digit_array.index(digit)
 
 		if value == -1 {
-			return error('Invalid character ${digit}')
+			return error('math.big: Invalid character ${digit}')
 		}
 		if value >= radix {
-			return error('Invalid character ${digit} for base ${radix}')
+			return error('math.big: Invalid character ${digit} for base ${radix}')
 		}
 	}
 }
@@ -972,10 +972,19 @@ pub fn (a Integer) factorial() Integer {
 	return product
 }
 
-// isqrt returns the closest integer square root of the given integer.
+// isqrt returns the closest integer square root of the integer `a`.
+//
+// WARNING: this method will panic if `a < 0`. Refer to isqrt_checked for a safer version.
+[inline]
 pub fn (a Integer) isqrt() Integer {
+	return a.isqrt_checked() or { panic(err) }
+}
+
+// isqrt returns the closest integer square root of the integer `a`.
+// An error is returned if `a < 0`.
+pub fn (a Integer) isqrt_checked() !Integer {
 	if a.signum < 0 {
-		panic('Cannot obtain square root of negative integer')
+		return error('math.big: Cannot calculate square root of negative integer')
 	}
 	if a.signum == 0 {
 		return a

vlib/math/big/special_array_ops_test.v

@@ -67,25 +67,25 @@ fn test_multiply_karatsuba_01() {
 	karatsuba_multiply_digit_array(a, b, mut c)
 	assert c == [u32(0xcaf2722e), 0x55eb2c5a, 0x3dc]
 
-	a_operand := integer_from_string('95484736384949495947362') or { panic('error') }
-	b_operand := integer_from_string('39474638493') or { panic('error') }
+	a_operand := integer_from_string('95484736384949495947362') or { panic(err) }
+	b_operand := integer_from_string('39474638493') or { panic(err) }
 	c = []u32{len: a_operand.digits.len + b_operand.digits.len, init: 0}
 	karatsuba_multiply_digit_array(a_operand.digits, b_operand.digits, mut c)
-	expected := integer_from_string('3769225450395285038584683507005466') or { panic('error') }
+	expected := integer_from_string('3769225450395285038584683507005466') or { panic(err) }
 	assert c == expected.digits
 }
 
 fn test_multiply_karatsuba_02() {
 	a := integer_from_string('53575430359313366047421252453000090528070240585276680372187519418517552556246806124659918940784792906379733645877657341259357264284615702179922887873492874019672838874121154927105373025311855709389770910765') or {
-		panic('error')
+		panic(err)
 	}
 	b := integer_from_string('977091076523237491790970633699383779582771973038531457285598238843271083830214915826312193418602834034688531898668229388286706296786321423078510899614439367') or {
-		panic('error')
+		panic(err)
 	}
 	mut c := []u32{len: a.digits.len + b.digits.len + 1, init: 0}
 	karatsuba_multiply_digit_array(a.digits, b.digits, mut c)
 	expected := integer_from_string('52348074924977237255285644820010078601114587486470740900886892189662650320988400136613780986308710610258879824881256666730655821800564143426560480113864123642197317383052431412305975584645367703594190956925565749714310612399025459615546540332117815550470167143256687163102859337019449165214274088466835988832405507818643018779158891710706073875995722420460085755') or {
-		panic('error')
+		panic(err)
 	}
 }
 
@@ -135,10 +135,10 @@ fn test_newton_divide_06() {
 
 fn test_newton_divide_07() {
 	a := integer_from_string('52348074924977237255285644820010078601114587486470740900886892189662650320988400136613780986308710610258879824881256666730655821800564143426560480113864123642197317383052431412305975584645367703594190956925565749714310612399025459615546540332117815550470167143256687163102859337019449165214274088466835988832405507818643018779158891710706073875995722420460085757') or {
-		panic('error')
+		panic(err)
 	}
 	b := integer_from_string('977091076523237491790970633699383779582771973038531457285598238843271083830214915826312193418602834034688531898668229388286706296786321423078510899614439367') or {
-		panic('error')
+		panic(err)
 	}
 	mut q := []u32{cap: a.digits.len - b.digits.len + 1}
 	mut r := []u32{cap: a.digits.len}