android rot13

before:
$ ./repo/android.sh kati -c -use_find_cache -kati_stats
*kati*: eval time: "34.677942345s"
*kati*: shell func time: "13.71144088s" 559
*kati*: dep build prepare time: "213.586963ms"
*kati*: 52737 variables
*kati*: 78461 explicit rules
*kati*: 0 implicit rules
*kati*: 1 suffix rules
*kati*: dep build time: "2.016057014s"
./repo/android.sh kati -c -use_find_cache -kati_stats  36.32s user 22.01s system 157% cpu 37.023 total

after:
$ ./repo/android.sh kati -c -use_find_cache -kati_stats
*kati*: eval time: "30.99209655s"
*kati*: shell func time: "10.133065433s" 385
*kati*: dep build prepare time: "236.542165ms"
*kati*: 52737 variables
*kati*: 78461 explicit rules
*kati*: 0 implicit rules
*kati*: 1 suffix rules
*kati*: dep build time: "1.880664823s"
./repo/android.sh kati -c -use_find_cache -kati_stats  36.65s user 18.09s system 164% cpu 33.218 total

1 files changed, 59 insertions, 0 deletions

diff --git a/func.go b/func.go
index 869aa39..a0d743b 100644
--- a/func.go
+++ b/func.go
@@ -764,6 +764,12 @@ func (f *funcShell) Compact() Value {
 		return f
 	}
 	// hack for android
+	if v, ok := matchAndroidRot13(expr); ok {
+		return &funcShellAndroidRot13{
+			funcShell: f,
+			v:         v,
+		}
+	}
 	if dir, ok := matchAndroidFindFileInDir(expr); ok {
 		androidFindCache.init()
 		return &funcShellAndroidFindFileInDir{
@@ -790,6 +796,59 @@ func (f *funcShell) Compact() Value {
 	return f
 }
 
+// pattern in repo/android/build/core/definisions.mk
+// rot13
+// echo $(1) | tr 'a-zA-Z' 'n-za-mN-ZA-M'
+func matchAndroidRot13(expr Expr) (Value, bool) {
+	// literal: "echo "
+	// paramref: 1
+	// literal: " | tr 'a-zA-Z' 'n-za-mN-ZA-M'"
+	if len(expr) != 3 {
+		return nil, false
+	}
+	if expr[0] != literal("echo ") {
+		return nil, false
+	}
+	if expr[1] != paramref(1) {
+		return nil, false
+	}
+	if expr[2] != literal(" | tr 'a-zA-Z' 'n-za-mN-ZA-M'") {
+		return nil, false
+	}
+	return expr[1], true
+}
+
+type funcShellAndroidRot13 struct {
+	*funcShell
+	v Value
+}
+
+func rot13(buf []byte) {
+	for i, b := range buf {
+		// tr 'a-zA-Z' 'n-za-mN-ZA-M'
+		if b >= 'a' && b <= 'z' {
+			b += 'n' - 'a'
+			if b > 'z' {
+				b -= 'z' - 'a' + 1
+			}
+		} else if b >= 'A' && b <= 'Z' {
+			b += 'N' - 'A'
+			if b > 'Z' {
+				b -= 'Z' - 'A' + 1
+			}
+		}
+		buf[i] = b
+	}
+}
+
+func (f *funcShellAndroidRot13) Eval(w io.Writer, ev *Evaluator) {
+	abuf := newBuf()
+	fargs := ev.args(abuf, f.v)
+	rot13(fargs[0])
+	w.Write(fargs[0])
+	freeBuf(abuf)
+}
+
 // pattern in repo/android/build/core/definitions.mk
 // find-subdir-assets
 // if [ -d $1 ] ; then cd $1 ; find ./ -not -name '.*' -and -type f -and -not -type l ; fi