strconv: fix %.2g, 40

Fixes #845.

R=rsc
CC=golang-dev
https://golang.org/cl/1673049

diff --git a/src/pkg/strconv/ftoa.go b/src/pkg/strconv/ftoa.go
index 656d81c98151ba5b1b55f5463f4e6ffedbb3111f..3659243c79054beb2bb3bdc0a953d65cc385a420 100644 (file)
--- a/src/pkg/strconv/ftoa.go
+++ b/src/pkg/strconv/ftoa.go
@@ -154,21 +154,27 @@ func genericFtoa(bits uint64, fmt byte, prec int, flt *floatInfo) string {
        case 'f':
                return fmtF(neg, d, prec)
        case 'g', 'G':
-               // trailing zeros are removed.
-               if prec > d.nd {
-                       prec = d.nd
+               // trailing fractional zeros in 'e' form will be trimmed.
+               eprec := prec
+               if eprec > d.nd && d.nd >= d.dp {
+                       eprec = d.nd
                }
                // %e is used if the exponent from the conversion
                // is less than -4 or greater than or equal to the precision.
                // if precision was the shortest possible, use precision 6 for this decision.
-               eprec := prec
                if shortest {
                        eprec = 6
                }
                exp := d.dp - 1
                if exp < -4 || exp >= eprec {
+                       if prec > d.nd {
+                               prec = d.nd
+                       }
                        return fmtE(neg, d, prec-1, fmt+'e'-'g')
                }
+               if prec > d.dp {
+                       prec = d.nd
+               }
                return fmtF(neg, d, max(prec-d.dp, 0))
        }
 

diff --git a/src/pkg/strconv/ftoa_test.go b/src/pkg/strconv/ftoa_test.go
index 85510b79c7bd2e64ec990b608db0a06596ae3b1f..cc01ccd7804e02b04e3e466a953b9f9c395c3c3a 100644 (file)
--- a/src/pkg/strconv/ftoa_test.go
+++ b/src/pkg/strconv/ftoa_test.go
@@ -34,6 +34,17 @@ var ftoatests = []ftoaTest{
        ftoaTest{200000, 'g', -1, "200000"},
        ftoaTest{2000000, 'g', -1, "2e+06"},
 
+       // g conversion and zero suppression
+       ftoaTest{400, 'g', 2, "4e+02"},
+       ftoaTest{40, 'g', 2, "40"},
+       ftoaTest{4, 'g', 2, "4"},
+       ftoaTest{.4, 'g', 2, "0.4"},
+       ftoaTest{.04, 'g', 2, "0.04"},
+       ftoaTest{.004, 'g', 2, "0.004"},
+       ftoaTest{.0004, 'g', 2, "0.0004"},
+       ftoaTest{.00004, 'g', 2, "4e-05"},
+       ftoaTest{.000004, 'g', 2, "4e-06"},
+
        ftoaTest{0, 'e', 5, "0.00000e+00"},
        ftoaTest{0, 'f', 5, "0.00000"},
        ftoaTest{0, 'g', 5, "0"},