A few weeks back, I posted about how I know that I have more to grok about Lisp macros. In that post, I needed to explain Lisp macros a bit for those not in the know. The example that I used was creating a jump table.
Geoff Wozniak just posted an article in his blog wherein he explores using a macro to do jump tables using an array of functions. He performed timing tests using Tim Bradshaw’s ncase macro versus case and switch.
The timing differences there are quite amazing. I’ve toyed around with optimizations quite a bit and have never seen Allegro outperform SBCL before this. It is also interesting that CLISP may already do this jump table optimization. I have never seen CLISP come anywhere close to SBCL or Allegro before this.
Update: Including timing numbers from my own machine
My machine is a 2.4GHz Intel-based Mac with 4GB of RAM. Here are the numbers that I get for this test. (All numbers in milliseconds).
| n | case | ncase | switch | |
| SBCL 1.0.29 | 10 | 166 | 149 | 207 |
| 100 | 185 | 146 | 191 | |
| 1000 | 572 | 147 | 207 | |
| CLISP 2.47 | 10 | 115 | 211 | 188 |
| 100 | 117 | 205 | 219 | |
| 1000 | 111 | 206 | 189 | |
| ACL 8.1 (heap-limited) | 10 | 10 | 20 | 90 |
| 100 | 20 | 10 | 90 | |
| 1000 | 1420 | 20 | 130 | |
| CMUCL 19f | 10 | 120 | 120 | 180 |
| 100 | 150 | 120 | 210 | |
| 1000 | 520 | 120 | 210 | |
| Clozure v1.3-r11936 | 10 | 19 | 15 | 128 |
| 100 | 108 | 14 | 130 | |
| 1000 | 1214 | 14 | 117 |
- With Allegro (ACL), I couldn’t compile easily. I had to load it, then compile it, then load the compiled version. If I just started Allegro and tried to compile, it complained that WITH-GENSYMS was an undefined function.
- With a heap-limited LispWorks, I failed to even compile the program. *shrug*