test/float_lit2.go: compute test values from first principles
These constants pass go/types constant conversions as well.
LGTM=r
R=r
CC=golang-codereviews
https://golang.org/cl/91590047
diff --git a/test/float_lit2.go b/test/float_lit2.go
index 30951a7..a68ba21 100644
--- a/test/float_lit2.go
+++ b/test/float_lit2.go
@@ -12,20 +12,75 @@
"fmt"
)
+const (
+ m32bits = 23 // number of float32 mantissa bits
+ e32max = 127 // max. float32 exponent
+ maxExp32 = e32max - m32bits
+ maxMant32 = 1<<(m32bits+1) - 1
+
+ maxFloat32_0 = (maxMant32 - 0) << maxExp32
+ maxFloat32_1 = (maxMant32 - 1) << maxExp32
+ maxFloat32_2 = (maxMant32 - 2) << maxExp32
+)
+
+func init() {
+ if maxExp32 != 104 {
+ panic("incorrect maxExp32")
+ }
+ if maxMant32 != 16777215 {
+ panic("incorrect maxMant32")
+ }
+ if maxFloat32_0 != 340282346638528859811704183484516925440 {
+ panic("incorrect maxFloat32_0")
+ }
+}
+
+const (
+ m64bits = 52 // number of float64 mantissa bits
+ e64max = 1023 // max. float64 exponent
+ maxExp64 = e64max - m64bits
+ maxMant64 = 1<<(m64bits+1) - 1
+
+ // These expressions are not permitted due to implementation restrictions.
+ // maxFloat64_0 = (maxMant64-0) << maxExp64
+ // maxFloat64_1 = (maxMant64-1) << maxExp64
+ // maxFloat64_2 = (maxMant64-2) << maxExp64
+
+ // These equivalent values were computed using math/big.
+ maxFloat64_0 = 1.7976931348623157e308
+ maxFloat64_1 = 1.7976931348623155e308
+ maxFloat64_2 = 1.7976931348623153e308
+)
+
+func init() {
+ if maxExp64 != 971 {
+ panic("incorrect maxExp64")
+ }
+ if maxMant64 != 9007199254740991 {
+ panic("incorrect maxMant64")
+ }
+}
+
var cvt = []struct {
val interface{}
binary string
}{
- {float32(-340282356779733661637539395458142568447), "-16777215p+104"},
- {float32(-340282326356119256160033759537265639424), "-16777214p+104"},
- {float32(340282326356119256160033759537265639424), "16777214p+104"},
- {float32(340282356779733661637539395458142568447), "16777215p+104"},
- {float64(-1.797693134862315807937289714053e+308), "-9007199254740991p+971"},
- {float64(-1.797693134862315708145274237317e+308), "-9007199254740991p+971"},
- {float64(-1.797693134862315608353258760581e+308), "-9007199254740990p+971"},
- {float64(1.797693134862315608353258760581e+308), "9007199254740990p+971"},
- {float64(1.797693134862315708145274237317e+308), "9007199254740991p+971"},
- {float64(1.797693134862315807937289714053e+308), "9007199254740991p+971"},
+
+ {float32(maxFloat32_0), fmt.Sprintf("%dp+%d", maxMant32-0, maxExp32)},
+ {float32(maxFloat32_1), fmt.Sprintf("%dp+%d", maxMant32-1, maxExp32)},
+ {float32(maxFloat32_2), fmt.Sprintf("%dp+%d", maxMant32-2, maxExp32)},
+
+ {float64(maxFloat64_0), fmt.Sprintf("%dp+%d", maxMant64-0, maxExp64)},
+ {float64(maxFloat64_1), fmt.Sprintf("%dp+%d", maxMant64-1, maxExp64)},
+ {float64(maxFloat64_2), fmt.Sprintf("%dp+%d", maxMant64-2, maxExp64)},
+
+ {float32(-maxFloat32_0), fmt.Sprintf("-%dp+%d", maxMant32-0, maxExp32)},
+ {float32(-maxFloat32_1), fmt.Sprintf("-%dp+%d", maxMant32-1, maxExp32)},
+ {float32(-maxFloat32_2), fmt.Sprintf("-%dp+%d", maxMant32-2, maxExp32)},
+
+ {float64(-maxFloat64_0), fmt.Sprintf("-%dp+%d", maxMant64-0, maxExp64)},
+ {float64(-maxFloat64_1), fmt.Sprintf("-%dp+%d", maxMant64-1, maxExp64)},
+ {float64(-maxFloat64_2), fmt.Sprintf("-%dp+%d", maxMant64-2, maxExp64)},
}
func main() {
