Six times faster than C

Re:Six times faster than C by sweetjuly on Friday July 07, 2023 @03:38AM (#36628481)

I'm sure people do that (even though it's not necessary per some year C standard) but generally the pattern is actually for converting things which are not already 0 or 1 into 0 or 1. For example, you might want to use it here:

    int num_empty_strings = !!(strlen(s1)) + !!(strlen(s2)) + !!(strlen(s3))

which is equivalent to:

    int num_empty_strings = (strlen(s1) != 0) + (strlen(s2) != 0) + (strlen(s3) != 0)

Which you use is really a matter of coding style.

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Re:Six times faster than C by stkdump on Friday July 07, 2023 @06:05AM (#36629525)

If we are being cryptic already, why not

    int num_empty_strings = !!*s1 + !!*s2 + !!*s3;

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Re:Six times faster than C by gjm11 on Friday July 07, 2023 @07:59AM (#36630373)

That isn't only more cryptic, it's also potentially a lot more efficient -- strlen takes time proportional to the length of the string, which of course you don't need to do if you only care whether or not the length is zero. You shouldn't use strlen for empty-string tests.

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Re:Six times faster than C by LegionMammal978 on Friday July 07, 2023 @08:32AM (#36630720)

In practice, GCC and Clang don't seem to have any issues inlining the necessary part of strlen at -O1 or higher (https://godbolt.org/z/rM198aYea). But MSVC inlines the empty-string case, while still calling out for nonempty strings, probably since it doesn't realize that the returned length will be nonzero.

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Re:Six times faster than C by stkdump on Saturday July 08, 2023 @02:17AM (#36641830)

I guess since strlen uses an unsigned size, which has specified overflow behavior the compiler not only has to proof the initial iteration, but also all the ULLONG_MAX+1 multiples, which of course refer to the same memory address. But maybe its harder for the optimizer to see.

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Re:Six times faster than C by areyousure on Friday July 07, 2023 @07:01AM (#36629912)

Note that your code computes the number of nonempty strings.

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