math: add lgamma; in-line special cases of acosh, nextafter

Added lgamma.go, tests and special cases.

R=rsc
CC=golang-dev
https://golang.org/cl/217060

src/pkg/math/Makefile

@@ -52,6 +52,7 @@ ALLGOFILES=\
 	fmod.go\
 	frexp.go\
 	hypot.go\
+	lgamma.go\
 	ldexp.go\
 	log.go\
 	log1p.go\

src/pkg/math/acosh.go

@@ -44,8 +44,11 @@ func Acosh(x float64) float64 {
 		Ln2   = 6.93147180559945286227e-01 // 0x3FE62E42FEFA39EF
 		Large = 1 << 28                    // 2^28
 	)
+	// TODO(rsc): Remove manual inlining of IsNaN
+	// when compiler does it for us
+	// first case is special case
 	switch {
-	case x < 1 || IsNaN(x):
+	case x < 1 || x != x: // x < 1 || IsNaN(x):
 		return NaN()
 	case x == 1:
 		return 0

src/pkg/math/all_test.go

@@ -286,7 +286,18 @@ var frexp = []fi{
 	fi{9.1265404584042750000e-01, 1},
 	fi{-5.4287029803597508250e-01, 4},
 }
-
+var lgamma = []fi{
+	fi{3.146492141244545774319734e+00, 1},
+	fi{8.003414490659126375852113e+00, 1},
+	fi{1.517575735509779707488106e+00, -1},
+	fi{-2.588480028182145853558748e-01, 1},
+	fi{1.1989897050205555002007985e+01, 1},
+	fi{6.262899811091257519386906e-01, 1},
+	fi{3.5287924899091566764846037e+00, 1},
+	fi{4.5725644770161182299423372e-01, 1},
+	fi{-6.363667087767961257654854e-02, 1},
+	fi{-1.077385130910300066425564e+01, -1},
+}
 var log = []float64{
 	1.605231462693062999102599e+00,
 	2.0462560018708770653153909e+00,
@@ -736,6 +747,21 @@ var hypotSC = []float64{
 	NaN(),
 }
 
+var vflgammaSC = []float64{
+	Inf(-1),
+	-3,
+	0,
+	Inf(1),
+	NaN(),
+}
+var lgammaSC = []fi{
+	fi{Inf(-1), 1},
+	fi{Inf(1), 1},
+	fi{Inf(1), 1},
+	fi{Inf(1), 1},
+	fi{NaN(), 1},
+}
+
 var vflogSC = []float64{
 	Inf(-1),
 	-Pi,
@@ -1229,6 +1255,19 @@ func TestLdexp(t *testing.T) {
 	}
 }
 
+func TestLgamma(t *testing.T) {
+	for i := 0; i < len(vf); i++ {
+		if f, s := Lgamma(vf[i]); !close(lgamma[i].f, f) || lgamma[i].i != s {
+			t.Errorf("Lgamma(%g) = %g, %d, want %g, %d\n", vf[i], f, s, lgamma[i].f, lgamma[i].i)
+		}
+	}
+	for i := 0; i < len(vflgammaSC); i++ {
+		if f, s := Lgamma(vflgammaSC[i]); !alike(lgammaSC[i].f, f) || lgammaSC[i].i != s {
+			t.Errorf("Lgamma(%g) = %g, %d, want %g, %d\n", vflgammaSC[i], f, s, lgammaSC[i].f, lgammaSC[i].i)
+		}
+	}
+}
+
 func TestLog(t *testing.T) {
 	for i := 0; i < len(vf); i++ {
 		a := Fabs(vf[i])
@@ -1632,6 +1671,12 @@ func BenchmarkLdexp(b *testing.B) {
 	}
 }
 
+func BenchmarkLgamma(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		Lgamma(2.5)
+	}
+}
+
 func BenchmarkLog(b *testing.B) {
 	for i := 0; i < b.N; i++ {
 		Log(.5)

src/pkg/math/nextafter.go

@@ -11,8 +11,10 @@ package math
 //	Nextafter(NaN, y) = NaN
 //	Nextafter(x, NaN) = NaN
 func Nextafter(x, y float64) (r float64) {
+	// TODO(rsc): Remove manual inlining of IsNaN
+	// when compiler does it for us
 	switch {
-	case IsNaN(x) || IsNaN(y): // special case
+	case x != x || y != y: // IsNaN(x) || IsNaN(y): // special case
 		r = NaN()
 	case x == y:
 		r = x