math: document special-cases behavior for Dim, Max and Min
Max returns +Inf if x or y is +Inf; else it returns NaN if either x or y is NaN. Max(-0, -0) returns -0.
Min returns -Inf if x or y is -Inf; else it returns NaN if either x or y is NaN. Min(+0, -0) returns -0.
Dim(+Inf, +Inf) = NaN, Dim(-Inf, -Inf) = NaN and Dim(NaN, anything) = NaN.
Also, change "conditions" to "cases" for Sin (missed it in previous CL).
R=rsc, dave
CC=golang-dev
https://golang.org/cl/5437137
diff --git a/src/pkg/math/dim.go b/src/pkg/math/dim.go
index d2eb52f..5701b14 100644
--- a/src/pkg/math/dim.go
+++ b/src/pkg/math/dim.go
@@ -5,15 +5,37 @@
package math
// Dim returns the maximum of x-y or 0.
+//
+// Special cases are:
+// Dim(+Inf, +Inf) = NaN
+// Dim(-Inf, -Inf) = NaN
+// Dim(x, NaN) = Dim(NaN, x) = NaN
func Dim(x, y float64) float64 {
- if x > y {
- return x - y
- }
- return 0
+ return Max(x-y, 0)
}
// Max returns the larger of x or y.
+//
+// Special cases are:
+// Max(x, +Inf) = Max(+Inf, x) = +Inf
+// Max(x, NaN) = Max(NaN, x) = NaN
+// Max(+0, ±0) = Max(±0, +0) = +0
+// Max(-0, -0) = -0
func Max(x, y float64) float64 {
+ // TODO(rsc): Remove manual inlining of IsNaN, IsInf
+ // when compiler does it for us
+ // special cases
+ switch {
+ case x > MaxFloat64 || y > MaxFloat64: // IsInf(x, 1) || IsInf(y, 1):
+ return Inf(1)
+ case x != x || y != y: // IsNaN(x) || IsNaN(y):
+ return NaN()
+ case x == 0 && x == y:
+ if Signbit(x) {
+ return y
+ }
+ return x
+ }
if x > y {
return x
}
@@ -21,7 +43,26 @@
}
// Min returns the smaller of x or y.
+//
+// Special cases are:
+// Min(x, -Inf) = Min(-Inf, x) = -Inf
+// Min(x, NaN) = Min(NaN, x) = NaN
+// Min(-0, ±0) = Min(±0, -0) = -0
func Min(x, y float64) float64 {
+ // TODO(rsc): Remove manual inlining of IsNaN, IsInf
+ // when compiler does it for us
+ // special cases
+ switch {
+ case x < -MaxFloat64 || y < -MaxFloat64: // IsInf(x, -1) || IsInf(y, -1):
+ return Inf(-1)
+ case x != x || y != y: // IsNaN(x) || IsNaN(y):
+ return NaN()
+ case x == 0 && x == y:
+ if Signbit(x) {
+ return x
+ }
+ return y
+ }
if x < y {
return x
}
