godoc: optimizations: don't call Write for 0-length data

- guard some calls to Write that frequently may have 0-length data
- fix an invariant

R=r
CC=golang-dev
https://golang.org/cl/4179041

diff --git a/src/cmd/godoc/godoc.go b/src/cmd/godoc/godoc.go
index ca9e2bb5425032e23991b330eeecec2b9549466d..86d1719805305e3da6f72301235009c8f5a58dee 100644 (file)
--- a/src/cmd/godoc/godoc.go
+++ b/src/cmd/godoc/godoc.go
@@ -274,7 +274,7 @@ func relativePath(path string) string {
 // ----------------------------------------------------------------------------
 // Tab conversion
 
-var spaces = []byte("                ") // 16 spaces seems like a good number
+var spaces = []byte("                                ") // 32 spaces seems like a good number
 
 const (
        indenting = iota
@@ -291,25 +291,31 @@ type tconv struct {
 
 func (p *tconv) writeIndent() (err os.Error) {
        i := p.indent
-       for i > len(spaces) {
+       for i >= len(spaces) {
                i -= len(spaces)
                if _, err = p.output.Write(spaces); err != nil {
                        return
                }
        }
-       _, err = p.output.Write(spaces[0:i])
+       // i < len(spaces)
+       if i > 0 {
+               _, err = p.output.Write(spaces[0:i])
+       }
        return
 }
 
 
 func (p *tconv) Write(data []byte) (n int, err os.Error) {
+       if len(data) == 0 {
+               return
+       }
        pos := 0 // valid if p.state == collecting
        var b byte
        for n, b = range data {
                switch p.state {
                case indenting:
                        switch b {
-                       case '\t', '\v':
+                       case '\t':
                                p.indent += *tabwidth
                        case '\n':
                                p.indent = 0
@@ -336,7 +342,7 @@ func (p *tconv) Write(data []byte) (n int, err os.Error) {
                }
        }
        n = len(data)
-       if p.state == collecting {
+       if pos < n && p.state == collecting {
                _, err = p.output.Write(data[pos:])
        }
        return
@@ -352,6 +358,10 @@ func writeNode(w io.Writer, fset *token.FileSet, x interface{}) {
        // to ensure a good outcome in most browsers (there may still
        // be tabs in comments and strings, but converting those into
        // the right number of spaces is much harder)
+       //
+       // TODO(gri) rethink printer flags - perhaps tconv can be eliminated
+       //           with an another printer mode (which is more efficiently
+       //           implemented in the printer than here with another layer)
        mode := printer.TabIndent | printer.UseSpaces
        (&printer.Config{mode, *tabwidth}).Fprint(&tconv{output: w}, fset, x)
 }