diff --git a/cmd/tools/vtest-cleancode.v b/cmd/tools/vtest-cleancode.v
index 2b56c89295..5dead592f3 100644
--- a/cmd/tools/vtest-cleancode.v
+++ b/cmd/tools/vtest-cleancode.v
@@ -60,6 +60,7 @@ const (
 		'vlib/cli/',
 		'vlib/flag/',
 		'vlib/gg/gg.v',
+		'vlib/math/big/',
 		'vlib/os/',
 		'vlib/semver/',
 		'vlib/strings/',
diff --git a/vlib/math/big/big.v b/vlib/math/big/big.v
index 0df769cc2a..055dc14c28 100644
--- a/vlib/math/big/big.v
+++ b/vlib/math/big/big.v
@@ -75,26 +75,28 @@ fn C.bignum_isqrt(a &Number, b &Number)
 // copy src number to dst number
 fn C.bignum_assign(dst &Number, src &Number)
 
-// //////////////////////////////////////////////////////////
-// conversion actions to/from big numbers:
+// new returns a bignum, initialized to 0
 pub fn new() Number {
 	return Number{}
 }
 
+// conversion actions to/from big numbers:
+// from_int converts an ordinary int number `i` to big.Number
 pub fn from_int(i int) Number {
 	n := Number{}
 	C.bignum_from_int(&n, i)
 	return n
 }
 
+// from_u64 converts an ordinary u64 number `u` to big.Number
 pub fn from_u64(u u64) Number {
 	n := Number{}
 	C.bignum_from_int(&n, u)
 	return n
 }
 
-// Converts a hex string to big.Number.
-pub fn from_string(input string) Number {
+// from_hex_string converts a hex string to big.Number
+pub fn from_hex_string(input string) Number {
 	mut s := input.trim_prefix('0x')
 	if s.len == 0 {
 		s = '0'
@@ -106,6 +108,17 @@ pub fn from_string(input string) Number {
 	return n
 }
 
+// from_string converts a decimal string to big.Number
+pub fn from_string(input string) Number {
+	mut n := from_int(0)
+	for _, c in input {
+		d := from_int(int(c - `0`))
+		n = (n * ten) + d
+	}
+	return n
+}
+
+// .int() converts (a small) big.Number `n` to an ordinary integer.
 pub fn (n Number) int() int {
 	r := C.bignum_to_int(&n)
 	return r
@@ -115,7 +128,7 @@ const (
 	ten = from_int(10)
 )
 
-// Decimal representation for the big unsigned integer number n.
+// .str returns a decimal representation of the big unsigned integer number n.
 pub fn (n Number) str() string {
 	if n.is_zero() {
 		return '0'
@@ -131,10 +144,11 @@ pub fn (n Number) str() string {
 	return digits.reverse().bytestr()
 }
 
+// .hexstr returns a hexadecimal representation of the bignum `n`
 pub fn (n Number) hexstr() string {
 	mut buf := [8192]byte{}
+	// NB: C.bignum_to_string(), returns the HEXADECIMAL representation of the bignum n
 	C.bignum_to_string(&n, buf, 8192)
-	// NB: bignum_to_string , returns the HEXADECIMAL representation of the bignum n
 	s := tos_clone(buf)
 	if s.len == 0 {
 		return '0'
diff --git a/vlib/math/big/big_test.v b/vlib/math/big/big_test.v
index da550160d1..9cfa7767ea 100644
--- a/vlib/math/big/big_test.v
+++ b/vlib/math/big/big_test.v
@@ -78,13 +78,24 @@ fn test_mod() {
 }
 
 fn test_from_str() {
-	assert big.from_string('').hexstr() == '0'
-	assert big.from_string('1').hexstr() == '1'
-	assert big.from_string('0').hexstr() == '0'
-	assert big.from_string('0x123').hexstr() == '123'
+	assert big.from_string('9870123').str() == '9870123'
+	assert big.from_string('').str() == '0'
+	assert big.from_string('0').str() == '0'
+	assert big.from_string('1').str() == '1'
+	for i := 1; i < 307; i += 61 {
+		input := '9'.repeat(i)
+		out := big.from_string(input).str()
+		// eprintln('>> i: $i input: $input.str()')
+		// eprintln('>> i: $i   out: $out.str()')
+		assert input == out
+	}
+}
+
+fn test_from_hex_str() {
+	assert big.from_hex_string('0x123').hexstr() == '123'
 	for i in 1 .. 33 {
 		input := 'e'.repeat(i)
-		out := big.from_string(input).hexstr()
+		out := big.from_hex_string(input).hexstr()
 		assert input == out
 	}
 	assert big.from_string('0').hexstr() == '0'
@@ -98,7 +109,7 @@ fn test_str() {
 	assert big.from_u64(4398046511104).str() == '4398046511104'
 	assert big.from_int(4294967295).str() == '18446744073709551615'
 	assert big.from_int(-1).str() == '18446744073709551615'
-	assert big.from_string('e'.repeat(80)).str() ==
+	assert big.from_hex_string('e'.repeat(80)).str() ==
 		'1993587900192849410235353592424915306962524220866209251950572167300738410728597846688097947807470'
 }