brian@digi-g.UUCP (Brian Westley) (09/06/84)
Here is a summary of the responses I received about the 'C' & Pascal & Modula, etc. modulus functions. I asked if (A mod B) should always fall within 0..B-1 even with negative A. It seems that the usual mathematical definition of modulus says yes, while most programming languages say no. Most programming languages really use remainder, such that: (A div B) * B + (A mod B) = A or: (A mod B) = A - (A div B) * B (This still depends on whether div truncates towards zero, or always down) Anyway, most languages return -2 for (-2 mod 3), while math modulus would say (-2 mod 3) is 1. Also, in math modulus, if B is negative, the answer is in B+1..0 Some langs don't allow B (or even A) to be negative. Wouldn't it be nice to have a modulus function, a remainder function, and two integer division functions, one truncating towards zero, the other always truncating to largest integer <= A/B ? I'm tired of having to do ((A+B) mod B) to get modulus to work the way I want it to....
joe@petsd.UUCP (Joe Orost) (09/07/84)
<>
The designers of Ada* saw some light in the mod/rem area. They put in both
"rem", which does what Fortran/C's MOD/% does, and "mod", which does what
all the math majors want.
Now all we need is a decent Ada* compiler.
[*Ada is a registered trademark of the U.S government, Ada Joint Program Office]
regards,
joe
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