strconv: fix `assert .f64() == 0`

vlib/builtin/string_test.v

@@ -936,3 +936,19 @@ fn test_index_any() {
 	assert x.index_any('ef') == 4
 	assert x.index_any('fe') == 4
 }
+
+fn test_string_f64() {
+	assert ''.f64() == 0
+	assert '123'.f64() == 123
+	assert '-123'.f64() == -123
+	assert '-123.456'.f64() == -123.456
+}
+
+const f32_epsilon = 0.0000000001
+
+fn test_string_f32() {
+	assert ''.f32() - 0 <= f32_epsilon
+	assert '123'.f32() - 123 < f32_epsilon
+	assert '-123'.f32() - (-123) < f32_epsilon
+	assert '-123.456'.f32() - (-123.456) <= f32_epsilon
+}

vlib/strconv/atof.c.v

@@ -78,9 +78,7 @@ fn sub96(s2 u32, s1 u32, s0 u32, d2 u32, d1 u32, d0 u32) (u32, u32, u32) {
 	return r2, r1, r0
 }
 
-/*
-Constants
-*/
+// Constants
 
 pub const (
 	//
@@ -118,9 +116,7 @@ pub const (
 	c_ten                 = u32(10)
 )
 
-/*
-Utility
-*/
+// Utility functions
 
 // NOTE: Modify these if working with non-ASCII encoding
 fn is_digit(x byte) bool {
@@ -135,10 +131,6 @@ fn is_exp(x byte) bool {
 	return (x == `E` || x == `e`) == true
 }
 
-/*
-Support struct
-*/
-
 /*
 String parser
 NOTE: #TOFIX need one char after the last char of the number
@@ -408,12 +400,13 @@ fn converter(mut pn PrepNumber) u64 {
 	return result
 }
 
-/*
-Public functions
-*/
+// Public functions
 
 // atof64 return a f64 from a string doing a parsing operation
 pub fn atof64(s string) f64 {
+	if s.len == 0 {
+		return 0
+	}
 	mut pn := PrepNumber{}
 	mut res_parsing := 0
 	mut res := Float64u{}