[Python-Dev] Simplify lnotab? (AST branch update) (original) (raw)

Greg Ewing greg.ewing at canterbury.ac.nz
Fri Oct 14 09:07:05 CEST 2005

Phillip J. Eby wrote:

A more compact scheme is possible, by using two tables - a bytecode->line number table, and a line number-> file table.

If you have to encode multiple files, you just offset their line numbers by the size of the other files,

More straightforwardly, the second table could just be a bytecode -> file number mapping. The filename is likely to change much less often than the line number, so this file would contain far fewer entries than the line number table. In the case of only one file, it would contain just a single entry, so it probably wouldn't even be worth the bother of special-casing that.

You could save a bit more by having two kinds of line number table, "small" (16-bit entries) and "large" (32-bit entries) depending on the size of the code object and range of line numbers. The small one would be sufficient for almost all code objects, so the most common case would use only about 4 bytes per line of code. That's only twice as much as the current scheme uses.

Greg

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