--- This message is a formal comment which was submitted to [EMAIL PROTECTED], following the requirements described at: http://www.r6rs.org/process.html --- submitter: Ben Harris <[EMAIL PROTECTED]> type: Enhancement priority: Minor component: Arithmetic version: 5.92 summary: bitwise-bit-count should return -ve on -ve argument.
As currently defined, bitwise-bit-count (page 41) is rather ugly, returning the number of set bits in non-negative arguments and the number of clear bits in negative ones. It would obviously be nicer if it were consistent, but this is made difficult by there being an infinite number of set bits in a negative number. This problem can be dodged by having bitwise-bit-count return the number of set bits mod0 infinity, or more prosaically, by returning the number of set bits in a non-negative argument, and _minus_ the number of clear bits in a negative one. This has some nicer properties than the current definition. In particular, setting a previously-clear bit in the argument uniformly increases the result by one, and clearing a previously-set bit decreases it. Also, for arguments that fit in a particular word size, the number of set bits in the argument represented in a word of that size can be obtained by taking the result modulo the word size, regardless of the sign of the argument. If there are uses for the current semantics, they're trivially obtained using "abs". The same change should be applied to fxbit-count on page 37. -- Ben Harris _______________________________________________ r6rs-discuss mailing list [email protected] http://lists.r6rs.org/cgi-bin/mailman/listinfo/r6rs-discuss
