strconv: fix e/g format (fix #22424) (#22430)

vlib/builtin/string_interpolation.v

@@ -512,6 +512,9 @@ fn (data &StrIntpData) process_str_intp_data(mut sb strings.Builder) {
 						f.free()
 						return
 					}
+					// NOTE: For 'g' and 'G' bf.len1 is the maximum number of significant digits.
+					// Not like 'e' or 'E', which is the number of digits after the decimal point.
+					bf.len1--
 					mut f := strconv.format_es(data.d.d_f32, bf)
 					if upper_case {
 						tmp := f
@@ -582,6 +585,9 @@ fn (data &StrIntpData) process_str_intp_data(mut sb strings.Builder) {
 						f.free()
 						return
 					}
+					// NOTE: For 'g' and 'G' bf.len1 is the maximum number of significant digits
+					// Not like 'e' or 'E', which is the number of digits after the decimal point.
+					bf.len1--
 					mut f := strconv.format_es(data.d.d_f64, bf)
 					if upper_case {
 						tmp := f
@@ -595,7 +601,6 @@ fn (data &StrIntpData) process_str_intp_data(mut sb strings.Builder) {
 			.si_e32 {
 				$if !nofloat ? {
 					// println("HERE: e32")
-					bf.len1 = 6
 					if use_default_str {
 						mut f := data.d.d_f32.str()
 						if upper_case {
@@ -623,7 +628,6 @@ fn (data &StrIntpData) process_str_intp_data(mut sb strings.Builder) {
 			.si_e64 {
 				$if !nofloat ? {
 					// println("HERE: e64")
-					bf.len1 = 6
 					if use_default_str {
 						mut f := data.d.d_f64.str()
 						if upper_case {

vlib/strconv/f64_str.c.v

@@ -22,7 +22,7 @@ https://github.com/cespare/ryu/tree/ba56a33f39e3bbbfa409095d0f9ae168a595feea
 
 @[direct_array_access]
 fn (d Dec64) get_string_64(neg bool, i_n_digit int, i_pad_digit int) string {
-	mut n_digit := i_n_digit + 1
+	mut n_digit := if i_n_digit < 1 { 1 } else { i_n_digit + 1 }
 	pad_digit := i_pad_digit + 1
 	mut out := d.m
 	mut d_exp := d.e
@@ -54,7 +54,10 @@ fn (d Dec64) get_string_64(neg bool, i_n_digit int, i_pad_digit int) string {
 		out += ten_pow_table_64[out_len - n_digit - 1] * 5 // round to up
 		out /= ten_pow_table_64[out_len - n_digit]
 		// println("out1:[$out] ${d.m / ten_pow_table_64[out_len - n_digit ]}")
-		if d.m / ten_pow_table_64[out_len - n_digit] < out {
+		// fix issue #22424
+		out_div := d.m / ten_pow_table_64[out_len - n_digit]
+		if out_div < out && dec_digits(out_div) < dec_digits(out) {
+			// from `99` to `100`, will need d_exp+1
 			d_exp++
 			n_digit++
 		}
@@ -74,13 +77,14 @@ fn (d Dec64) get_string_64(neg bool, i_n_digit int, i_pad_digit int) string {
 		x++
 	}
 
+	// fix issue #22424
 	// no decimal digits needed, end here
-	if i_n_digit == 0 {
-		unsafe {
-			buf[i] = 0
-			return tos(&u8(&buf[0]), i)
-		}
-	}
+	// if i_n_digit == 0 {
+	//	unsafe {
+	//		buf[i] = 0
+	//		return tos(&u8(&buf[0]), i)
+	//	}
+	//}
 
 	if out_len >= 1 {
 		buf[y - x] = `.`
@@ -365,7 +369,7 @@ pub fn f64_to_str_pad(f f64, n_digit int) string {
 	neg := (u >> (mantbits64 + expbits64)) != 0
 	mant := u & ((u64(1) << mantbits64) - u64(1))
 	exp := (u >> mantbits64) & ((u64(1) << expbits64) - u64(1))
-	// println("s:${neg} mant:${mant} exp:${exp} float:${f} byte:${u1.u:016lx}")
+	// unsafe { println("s:${neg} mant:${mant} exp:${exp} float:${f} byte:${u1.u:016x}") }
 
 	// Exit early for easy cases.
 	if exp == maxexp64 || (exp == 0 && mant == 0) {

vlib/strconv/format_test.v

@@ -126,3 +126,22 @@ fn test_remove_tail_zeros() {
 	assert strconv.remove_tail_zeros('1234') == '1234'
 	assert strconv.remove_tail_zeros('1.00000000007') == '1.00000000007'
 }
+
+fn test_g_format() {
+	a := 1234.56789000e10
+	assert '${a:1.0g}' == '1e+13'
+	assert '${a:1.1g}' == '1e+13'
+	assert '${a:1.2g}' == '1.2e+13'
+	assert '${a:1.3g}' == '1.23e+13'
+	assert '${a:1.4g}' == '1.235e+13'
+	assert '${a:1.5g}' == '1.2346e+13'
+	assert '${a:1.6g}' == '1.23457e+13'
+	assert '${a:1.7g}' == '1.234568e+13'
+	assert '${a:1.8g}' == '1.2345679e+13'
+	assert '${a:1.9g}' == '1.23456789e+13'
+	assert '${a:1.10g}' == '1.23456789e+13'
+	assert '${a:1.11g}' == '1.23456789e+13'
+	assert '${a:1.12g}' == '1.23456789e+13'
+
+	// TODO: e format not support due to issue #22429
+}