math: added ilogb, logb, remainder, tests and special conditions
Also added expm1_386 and remainder_386; shortened exp_386
R=rsc
CC=golang-dev
https://golang.org/cl/217109
diff --git a/src/pkg/math/logb.go b/src/pkg/math/logb.go
new file mode 100644
index 0000000..acda15d
--- /dev/null
+++ b/src/pkg/math/logb.go
@@ -0,0 +1,47 @@
+// Copyright 2010 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package math
+
+// Logb(x) returns the binary logarithm of non-zero x.
+//
+// Special cases are:
+// Logb(±Inf) = +Inf
+// Logb(0) = -Inf
+// Logb(NaN) = NaN
+func Logb(x float64) float64 {
+ // TODO(rsc): Remove manual inlining of IsNaN, IsInf
+ // when compiler does it for us
+ // special cases
+ switch {
+ case x == 0:
+ return Inf(-1)
+ case x < -MaxFloat64 || x > MaxFloat64: // IsInf(x, 0):
+ return Inf(1)
+ case x != x: // IsNaN(x):
+ return x
+ }
+ return float64(int((Float64bits(x)>>shift)&mask) - bias)
+}
+
+// Ilogb(x) returns the binary logarithm of non-zero x as an integer.
+//
+// Special cases are:
+// Ilogb(±Inf) = MaxInt32
+// Ilogb(0) = MinInt32
+// Ilogb(NaN) = MaxInt32
+func Ilogb(x float64) int {
+ // TODO(rsc): Remove manual inlining of IsNaN, IsInf
+ // when compiler does it for us
+ // special cases
+ switch {
+ case x == 0:
+ return MinInt32
+ case x != x: // IsNaN(x):
+ return MaxInt32
+ case x < -MaxFloat64 || x > MaxFloat64: // IsInf(x, 0):
+ return MaxInt32
+ }
+ return int((Float64bits(x)>>shift)&mask) - bias
+}
