internal/strconv: add tests and benchmarks for ftoaFixed

ftoaFixed is in the next CL; this proves the tests are correct
against the current implementation, and it adds a benchmark
for comparison with the new implementation.

Change-Id: I7ac8a1f699b693ea6d11a7122b22fc70cc135af6
Reviewed-on: https://go-review.googlesource.com/c/go/+/717181
Auto-Submit: Russ Cox <rsc@golang.org>
Reviewed-by: Alan Donovan <adonovan@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

Author: rsc

src/internal/strconv/fp_test.go

@@ -99,12 +99,14 @@ func TestFp(t *testing.T) {
 	s := bufio.NewScanner(strings.NewReader(testfp))
 	for lineno := 1; s.Scan(); lineno++ {
 		line := s.Text()
-		if len(line) == 0 || line[0] == '#' {
+		line, _, _ = strings.Cut(line, "#")
+		line = strings.TrimSpace(line)
+		if line == "" {
 			continue
 		}
 		a := strings.Split(line, " ")
 		if len(a) != 4 {
-			t.Error("testdata/testfp.txt:", lineno, ": wrong field count")
+			t.Errorf("testdata/testfp.txt:%d: wrong field count", lineno)
 			continue
 		}
 		var s string
@@ -114,22 +116,21 @@ func TestFp(t *testing.T) {
 			var ok bool
 			v, ok = myatof64(a[2])
 			if !ok {
-				t.Error("testdata/testfp.txt:", lineno, ": cannot atof64 ", a[2])
+				t.Errorf("testdata/testfp.txt:%d: cannot atof64 %s", lineno, a[2])
 				continue
 			}
 			s = fmt.Sprintf(a[1], v)
 		case "float32":
 			v1, ok := myatof32(a[2])
 			if !ok {
-				t.Error("testdata/testfp.txt:", lineno, ": cannot atof32 ", a[2])
+				t.Errorf("testdata/testfp.txt:%d: cannot atof32 %s", lineno, a[2])
 				continue
 			}
 			s = fmt.Sprintf(a[1], v1)
 			v = float64(v1)
 		}
 		if s != a[3] {
-			t.Error("testdata/testfp.txt:", lineno, ": ", a[0], " ", a[1], " ", a[2], " (", v, ") ",
-				"want ", a[3], " got ", s)
+			t.Errorf("testdata/testfp.txt:%d: %s %s %s %s: have %s want %s", lineno, a[0], a[1], a[2], a[3], s, a[3])
 		}
 	}
 	if s.Err() != nil {

src/internal/strconv/ftoa_test.go

@@ -5,9 +5,9 @@
 package strconv_test
 
 import (
+	. "internal/strconv"
 	"math"
 	"math/rand"
-	. "internal/strconv"
 	"testing"
 )
 
@@ -294,15 +294,21 @@ var ftoaBenches = []struct {
 
 	{"64Fixed1", 123456, 'e', 3, 64},
 	{"64Fixed2", 123.456, 'e', 3, 64},
+	{"64Fixed2.5", 1.2345e+06, 'e', 3, 64},
 	{"64Fixed3", 1.23456e+78, 'e', 3, 64},
 	{"64Fixed4", 1.23456e-78, 'e', 3, 64},
+	{"64Fixed5Hard", 4.096e+25, 'e', 5, 64}, // needs divisiblePow5(..., 20)
 	{"64Fixed12", 1.23456e-78, 'e', 12, 64},
 	{"64Fixed16", 1.23456e-78, 'e', 16, 64},
 	// From testdata/testfp.txt
 	{"64Fixed12Hard", math.Ldexp(6965949469487146, -249), 'e', 12, 64},
 	{"64Fixed17Hard", math.Ldexp(8887055249355788, 665), 'e', 17, 64},
 	{"64Fixed18Hard", math.Ldexp(6994187472632449, 690), 'e', 18, 64},
 
+	{"64FixedF1", 123.456, 'f', 6, 64},
+	{"64FixedF2", 0.0123, 'f', 6, 64},
+	{"64FixedF3", 12.3456, 'f', 2, 64},
+
 	// Trigger slow path (see issue #15672).
 	// The shortest is: 8.034137530808823e+43
 	{"Slowpath64", 8.03413753080882349e+43, 'e', -1, 64},