Am Sonntag, den 21.08.2011, 19:38 -0400 schrieb Terry Reedy: > On 8/21/2011 7:17 PM, Andreas Löscher wrote: > > Am Sonntag, den 21.08.2011, 14:52 -0400 schrieb Roy Smith: > >> In article<mailman.282.1313951079.27778.python-l...@python.org>, > >> Christian Heimes<li...@cheimes.de> wrote: > >> > >>> Am 21.08.2011 19:27, schrieb Andreas Lscher: > >>>> As for using Integers, the first case (line 1319 and 1535) are true and > >>>> there is no difference in Code. However, Python uses a huge switch-case > >>>> construct to execute it's opcodes and INPLACE_ADD cames after > >>>> BINARY_ADD, hence the difference in speed. > >>> > >>> I don't think that's the reason. Modern compiles turn a switch statement > >>> into a jump or branch table rather than a linear search like chained > >>> elif statements. > >> > >> This is true even for very small values of "modern". I remember the > >> Unix v6 C compiler (circa 1977) was able to do this. > > > > What is the difference in speed between a jump table that is searched > > from top to bottom in comparison to an ordinary if-then-elif...? The > > difference can only be in the search algorithm regarding the table. > > Without optimization (linear search) both are the same. If the compiler > > applies some magic the difference can be relevant (linear complexity for > > if-then-elif... and O(1) if you would use a dictionary). > > A jump or branch table is applicable when the case value values are all > small ints, like bytes or less. For C, the table is simply an array of > pointers (addressess, with entries for unused byte codes would be a void > pointer). Hence, O(1) access. > https://secure.wikimedia.org/wikipedia/en/wiki/Jump_table > > > Hence the executed code for integers is the same, there must be a slower > > path to the code of BINARY_ADD than to INPLACE_ADD. > > > > How would such an jump table work to behave the same liek a > > switch-case-statement? Beware, that things like > > > > case PRINT_NEWLINE_TO: > > 1802 w = stream = POP(); > > 1803 /* fall through to PRINT_NEWLINE */ > > add jump to address of the code for PRINT_NEWLINE > > > 1804 > > 1805 case PRINT_NEWLINE: > > > > must be supported. >
:-) too easy or too late thanks -- http://mail.python.org/mailman/listinfo/python-list
