strconv: produce a maximum of 8 digits after the . for f32.str() (fix #25141) (#25144)

Author: spytheman

vlib/strconv/f32_f64_to_string_test.v

@@ -172,3 +172,35 @@ fn test_float_to_str() {
 	// assert ftoa.f64_to_str(0.3456789123456, 4)=="3.4568e-01"
 	// assert ftoa.f32_to_str(0.345678, 3)=="3.457e-01"
 }
+
+fn test_issue_25141_1() {
+	assert strconv.ftoa_long_32(0.1234567901) == '0.12345679'
+}
+
+fn test_issue_25141_2() {
+	assert strconv.f32_to_str_l(math.f32_from_bits(1055100472)) == '0.44444442'
+}
+
+fn test_issue_25141_3() {
+	assert strconv.f32_to_str_l(math.f32_from_bits(1055100473)) == '0.44444445'
+}
+
+fn test_issue_25141_4() {
+	assert strconv.f32_to_str_l(math.f32_from_bits(1055100474)) == '0.44444448'
+}
+
+fn test_issue_25141_5() {
+	assert strconv.f32_to_str_l(math.f32_from_bits(1055100475)) == '0.4444445'
+}
+
+fn test_issue_25141_0001() {
+	assert strconv.f32_to_str_l(math.f32_from_bits(953267991)) == '0.0001'
+	assert strconv.f32_to_str_l(math.f32_from_bits(953267992)) == '0.000100000005'
+	assert strconv.f32_to_str_l(math.f32_from_bits(953267993)) == '0.00010000001'
+	assert strconv.f32_to_str_l(math.f32_from_bits(953267994)) == '0.00010000002'
+	assert strconv.f32_to_str_l(math.f32_from_bits(953267995)) == '0.00010000003'
+	assert strconv.f32_to_str_l(math.f32_from_bits(953267996)) == '0.000100000034'
+	assert strconv.f32_to_str_l(math.f32_from_bits(953267997)) == '0.00010000004'
+	assert strconv.f32_to_str_l(math.f32_from_bits(953267998)) == '0.00010000005'
+	assert strconv.f32_to_str_l(math.f32_from_bits(953267999)) == '0.000100000056'
+}

vlib/strconv/f32_str_should_be_different_test.v

@@ -0,0 +1,35 @@
+import math
+
+fn test_around() {
+	// do not pass 0
+	for f in [f32(1e-12), 1e-9, 1e-6, 1e-4, 0.1, 0.2, 0.5, 1, 2, 5, 10, 1e6, 1e7, 1e9, 1e12] {
+		check_around(f, 1000)
+	}
+}
+
+fn check_around(fval f32, total int) {
+	check(fval, total)
+	check(-fval, total)
+}
+
+fn check(fval f32, total int) {
+	middle_bits := math.f32_bits(fval)
+	start_bits := middle_bits - u32(total / 2)
+	end_bits := middle_bits + u32(total / 2)
+	min, max := if start_bits < end_bits { start_bits, end_bits } else { end_bits, start_bits }
+	println('> check_around ${total} f32 values around fval: ${fval:26.12f}, middle_bits for fval: ${middle_bits:12} | min: ${min:12} | max: ${max:12}')
+	for ux in min .. max {
+		x := math.f32_from_bits(ux)
+		if math.is_nan(x) {
+			continue
+		}
+		uy := ux - 1
+		y := math.f32_from_bits(uy)
+		if x == y {
+			continue
+		}
+		sx := x.str()
+		sy := y.str()
+		assert sx != sy, 'math.f32_from_bits(${ux})'
+	}
+}

vlib/strconv/ftoa.c.v

@@ -19,32 +19,28 @@ https://github.com/cespare/ryu/tree/ba56a33f39e3bbbfa409095d0f9ae168a595feea
 */
 
 // ftoa_64 returns a string in scientific notation with max 17 digits after the dot.
-//
 // Example: assert strconv.ftoa_64(123.1234567891011121) == '1.2312345678910111e+02'
 @[inline]
 pub fn ftoa_64(f f64) string {
 	return f64_to_str(f, 17)
 }
 
 // ftoa_long_64 returns `f` as a `string` in decimal notation with a maximum of 17 digits after the dot.
-//
 // Example: assert strconv.f64_to_str_l(123.1234567891011121) == '123.12345678910111'
 @[inline]
 pub fn ftoa_long_64(f f64) string {
 	return f64_to_str_l(f)
 }
 
 // ftoa_32 returns a `string` in scientific notation with max 8 digits after the dot.
-//
 // Example: assert strconv.ftoa_32(34.1234567) == '3.4123455e+01'
 @[inline]
 pub fn ftoa_32(f f32) string {
 	return f32_to_str(f, 8)
 }
 
-// ftoa_long_32 returns `f` as a `string` in decimal notation with a maximum of 6 digits after the dot.
-//
-// Example: assert strconv.ftoa_long_32(34.1234567) == '34.12346'
+// ftoa_long_32 returns `f` as a `string` in decimal notation with a maximum of 8 digits after the dot.
+// Example: assert strconv.ftoa_long_32(0.1234567901) == '0.12345679'
 @[inline]
 pub fn ftoa_long_32(f f32) string {
 	return f32_to_str_l(f)

vlib/strconv/utilities.c.v

@@ -23,24 +23,24 @@ f64 to string with string format
 */
 
 // TODO: Investigate precision issues
-// f32_to_str_l returns `f` as a `string` in decimal notation with a maximum of 6 digits after the dot.
-//
-// Example: assert strconv.f32_to_str_l(34.1234567) == '34.12346'
+// f32_to_str_l returns `f` as a `string` in decimal notation with a maximum of 8 digits after the dot.
+// Example: assert strconv.f32_to_str_l(0.1234567891) == '0.12345679'
+// Example: assert strconv.f32_to_str_l(34.1234567891) == '34.123455'
 @[manualfree]
 pub fn f32_to_str_l(f f32) string {
-	s := f32_to_str(f, 6)
+	s := f32_to_str(f, 8)
 	res := fxx_to_str_l_parse(s)
 	unsafe { s.free() }
 	return res
 }
 
-// f32_to_str_l_with_dot returns `f` as a `string` in decimal notation with a maximum of 6 digits after the dot.
+// f32_to_str_l_with_dot returns `f` as a `string` in decimal notation with a maximum of 8 digits after the dot.
 // If the decimal digits after the dot are zero, a '.0' is appended for clarity.
 //
 // Example: assert strconv.f32_to_str_l_with_dot(34.) == '34.0'
 @[manualfree]
 pub fn f32_to_str_l_with_dot(f f32) string {
-	s := f32_to_str(f, 6)
+	s := f32_to_str(f, 8)
 	res := fxx_to_str_l_parse_with_dot(s)
 	unsafe { s.free() }
 	return res

vlib/v/slow_tests/repl/fn_calls.repl

@@ -4,7 +4,7 @@ fn test() { println('foo') } fn test2(a int) { println(a) }
 test()
 test2(123)
 ===output===
--0.2623749
+-0.26237485
 0.7376251
 foo
 123