strconv: fix float scientific notation (fix #26045) (#26046)

Author: kbkpbot

vlib/strconv/f32_f64_to_string_test.v

@@ -63,17 +63,17 @@ fn test_float_to_str() {
 		'nan',
 		'+inf',
 		'-inf',
-		'1.e+00',
-		'-1.e+00',
-		'1.e+01',
-		'-1.e+01',
-		'3.e-01',
-		'-3.e-01',
-		'1.e+06',
+		'1e+00',
+		'-1e+00',
+		'1e+01',
+		'-1e+01',
+		'3e-01',
+		'-3e-01',
+		'1e+06',
 		'1.234567e+05',
 		'1.23e+37',
 		'-1.2345e+02',
-		'1.e+23',
+		'1e+23',
 		'1.1754944e-38', // aprox from 1.1754943508 × 10−38,
 		'3.4028235e+38',
 		'3.8326058e+17',
@@ -115,25 +115,25 @@ fn test_float_to_str() {
 		'nan',
 		'+inf',
 		'-inf',
-		'1.e+00',
-		'-1.e+00',
-		'1.e+01',
-		'-1.e+01',
-		'3.e-01',
-		'-3.e-01',
-		'1.e+06',
+		'1e+00',
+		'-1e+00',
+		'1e+01',
+		'-1e+01',
+		'3e-01',
+		'-3e-01',
+		'1e+06',
 		'1.234567e+05',
 		'1.23e+47',
 		'-1.2345e+02',
-		'1.e+23',
+		'1e+23',
 		'2.2250738585072014e-308',
 		'3.4028234663852886e+38',
 		'3.8326057576481645e+17',
 		'3.8326057576481645e+17',
 		'1.23e+302', // this test is failed from C sprintf!!
 		'1.23e-298',
-		'5.e-324',
-		'-5.e-324',
+		'5e-324',
+		'-5e-324',
 	]
 
 	// test f32

vlib/strconv/f32_str.c.v

@@ -101,11 +101,11 @@ pub fn (d Dec32) get_string_32(neg bool, i_n_digit int, i_pad_digit int) string
 		}
 	}
 
-	if out_len >= 1 {
+	if out_len > 1 || fw_zeros > 0 {
 		buf[y - x] = `.`
-		x++
 		i++
 	}
+	x++
 
 	if y - x >= 0 {
 		buf[y - x] = `0` + u8(out % 10)

vlib/strconv/f64_str.c.v

@@ -86,11 +86,11 @@ fn (d Dec64) get_string_64(neg bool, i_n_digit int, i_pad_digit int) string {
 	//	}
 	//}
 
-	if out_len >= 1 {
+	if out_len > 1 || fw_zeros > 0 {
 		buf[y - x] = `.`
-		x++
 		i++
 	}
+	x++
 
 	if y - x >= 0 {
 		buf[y - x] = `0` + u8(out % 10)