Rename the zigzag package to varint/zigzag.

varint/varint.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// Package varint implements a variable-width byte encoding of integers.
+// Package varint implements a variable-width encoding of unsigned integers.
 //
 // It is the same format used by protocol buffers. The format is described at
 // http://code.google.com/apis/protocolbuffers/docs/encoding.html

zigzag/Makefile → varint/zigzag/Makefile

@@ -4,7 +4,7 @@
 
 include $(GOROOT)/src/Make.inc
 
-TARG=snappy-go.googlecode.com/hg/zigzag
+TARG=snappy-go.googlecode.com/hg/varint/zigzag
 GOFILES=\
 	zigzag.go\
 

zigzag/zigzag.go → varint/zigzag/zigzag.go

@@ -4,20 +4,29 @@
 
 // Package zigzag implements the zigzag mapping between signed and unsigned
 // integers:
-//	+0 <--> 0
-//	-1 <--> 1
-//	+1 <--> 2
-//	-2 <--> 3
-//	+2 <--> 4
+//	+0 <-> 0
+//	-1 <-> 1
+//	+1 <-> 2
+//	-2 <-> 3
+//	+2 <-> 4
+//	etcetera
 //
 // It is the same format used by protocol buffers. The format is described at
 // http://code.google.com/apis/protocolbuffers/docs/encoding.html
 package zigzag
 
+// Itou64 maps a signed integer to an unsigned integer.
+// If i >= 0, the result is 2*i.
+// If i < 0, the result is -2*i - 1.
+// The formulae above are in terms of ideal integers, with no overflow.
 func Itou64(i int64) uint64 {
 	return uint64(i<<1 ^ i>>63)
 }
 
+// Utoi64 maps an unsigned integer to a signed integer.
+// If u%2 == 0, the result is u/2.
+// If u%2 == 1, the result is -(u+1)/2.
+// The formulae above are in terms of ideal integers, with no overflow.
 func Utoi64(u uint64) int64 {
 	return int64(u>>1) ^ -int64(u&1)
 }