A Regular Expression Matcher (2007)

Post by eru » Mon, Aug 01, 2016, 11:29 AM UTC

jake-low wrote: post #13

gfody wrote: post #12

Earlier quoted context omitted.

I keep one-line blocks unbraced when possible and my reasoning is definitely not to feel like a tough macho man. It's more like a mild form of OCD where any syntax that's not necessary just bothers me if I don't omit it.

Reductio ad absurdum: I assume your variable names are single-letter, your Python is indented only one space per block level and every C program is a one-liner? You should check out the Code Golf stackexchange; you'd do well. Kidding aside, I can appreciate your feeling of OCD (I fight that urge too) but remember that most syntax is for humans, not machines. Using braces communicates intent to the reader; omitting th…

Post by Someone » Mon, Aug 01, 2016, 4:22 PM UTC

groovy2shoes wrote: post #25

Someone wrote: post #22

Earlier quoted context omitted.

"Is this: while (foo != '\0') { bar++ = foo++; } really that much nicer than this: while (i != len) { bar[i++] = foo[i++]; }" Not visually, but the latter increments i twice in every loop :-). It also typically uses an extra register and requires an explicit 'compare with zero'. Both mattered more 40+ years ago.

> the latter increments i twice in every loop :-). D'oh! Good catch. That's what I get for coding without testing at 3am... Just realized `foo != '\0'` should be `* foo != '\0'`, too. Derp. > It also typically uses an extra register and requires an explicit 'compare with zero'. Okay, I see the extra register, but I'm lost on any extra comparisons versus the pointer-arithmetic version. The pointer version still has to…

    while (*ra++ = *rb++);
    

    L16:
        movb        (r10)+,(r11)+
        jeql        L17
        jbr         L16
    L17:

Post by groovy2shoes » Tue, Aug 02, 2016, 5:22 PM UTC

Someone wrote: post #33

groovy2shoes wrote: post #25

Earlier quoted context omitted.

> the latter increments i twice in every loop :-). D'oh! Good catch. That's what I get for coding without testing at 3am... Just realized `foo != '\0'` should be `* foo != '\0'`, too. Derp. > It also typically uses an extra register and requires an explicit 'compare with zero'. Okay, I see the extra register, but I'm lost on any extra comparisons versus the pointer-arithmetic version. The pointer version still has to…

"The pointer version still has to test for the nul character anyway, right?" Some architectures set the zero flag on memory loads. I think the PDP is one of them. Google gives me https://groups.google.com/forum/m/#!topic/net.lang.c/LKAYbzX... , which claims that while (*ra++ = *rb++); compiles to L16: movb (r10)+,(r11)+ jeql L17 jbr L16 L17: If you do i != len , you need an extra comparison instruction.