Speed up WriteUtf8 in the case where the output buffer is large enough.

Speed up WriteUtf8 in the case where the output buffer is large enough.
Committed: https://code.google.com/p/v8/source/detail?r=11104

[Erik Corry, 2012-03-13 10:41:17]

Benchmark results:

  Short Ascii (plenty): 16ms                                     |  Short Ascii
(plenty): 15ms                                     
  Short Unicode (plenty): 81ms                                   |  Short
Unicode (plenty): 36ms                                   
  Prepend Unicode (plenty): 46ms                                 |  Prepend
Unicode (plenty): 15ms                                 
  Unbalanced left (plenty): 10ms                                 |  Unbalanced
left (plenty): 11ms                                 
  Unbalanced right (plenty): 10ms                                |  Unbalanced
right (plenty): 10ms
  Unbalanced Unicode left (plenty): 16ms                         |  Unbalanced
Unicode left (plenty): 10ms                         
  Unbalanced Unicode right (plenty): 26ms                        |  Unbalanced
Unicode right (plenty): 9ms                         
  Unbalanced long left (plenty): 13ms                            |  Unbalanced
long left (plenty): 13ms
  Unbalanced long right (plenty): 14ms                           |  Unbalanced
long right (plenty): 13ms                           
  Unbalanced Unicode long left (plenty): 658ms                   |  Unbalanced
Unicode long left (plenty): 89ms                    
  Unbalanced Unicode long right (plenty): 620ms                  |  Unbalanced
Unicode long right (plenty): 100ms                  
  Prepend Unbalanced long left (plenty): 213ms                   |  Prepend
Unbalanced long left (plenty): 13ms                    
  Prepend Unbalanced long right (plenty): 205ms                  |  Prepend
Unbalanced long right (plenty): 13ms                   
  Unbalanced Unicode long left hint-many (plenty): 286ms         |  Unbalanced
Unicode long left hint-many (plenty): 89ms          
  Unbalanced Unicode long right hint-many (plenty): 287ms        |  Unbalanced
Unicode long right hint-many (plenty): 99ms         
  Short Ascii (just enough): 16ms                                |  Short Ascii
(just enough): 15ms                                
  Short Unicode (just enough): 93ms                              |  Short
Unicode (just enough): 74ms                              
  Prepend Unicode (just enough): 47ms                            |  Prepend
Unicode (just enough): 20ms                            
  Unbalanced left (just enough): 10ms                            |  Unbalanced
left (just enough): 9ms                             
  Unbalanced right (just enough): 9ms                            |  Unbalanced
right (just enough): 9ms
  Unbalanced Unicode left (just enough): 20ms                    |  Unbalanced
Unicode left (just enough): 12ms                    
  Unbalanced Unicode right (just enough): 31ms                   |  Unbalanced
Unicode right (just enough): 18ms                   
  Unbalanced long left (just enough): 13ms                       |  Unbalanced
long left (just enough): 13ms
  Unbalanced long right (just enough): 13ms                      |  Unbalanced
long right (just enough): 13ms
  Unbalanced Unicode long left (just enough): 695ms              |  Unbalanced
Unicode long left (just enough): 198ms              
  Unbalanced Unicode long right (just enough): 654ms             |  Unbalanced
Unicode long right (just enough): 203ms             
  Prepend Unbalanced long left (just enough): 193ms              |  Prepend
Unbalanced long left (just enough): 14ms               
  Prepend Unbalanced long right (just enough): 183ms             |  Prepend
Unbalanced long right (just enough): 14ms              
  Unbalanced Unicode long left hint-many (just enough): 323ms    |  Unbalanced
Unicode long left hint-many (just enough): 195ms    
  Unbalanced Unicode long right hint-many (just enough): 323ms   |  Unbalanced
Unicode long right hint-many (just enough): 204ms

[fschneider, 2012-03-20 09:45:49]

LGTM.

It would be a good to add a test-case for the different cases in into
cctest/test-api.

https://chromiumcodereview.appspot.com/9696032/diff/7001/src/api.cc
File src/api.cc (right):

https://chromiumcodereview.appspot.com/9696032/diff/7001/src/api.cc#newcode3745
src/api.cc:3745: }
Accidental fall-through here?

[Erik Corry, 2012-03-21 13:50:39]

Nice catch.  Test improved to cover sliced strings, which uncovered another bug!