String compare performance

[bearophile]

denis.spir

> What's your diagnostic on why basic string compare parforms the way it does?

I prefer the numbers and asm listings speak for themselves, because my diagnostic sometimes is wrong. But I guess it's caused by three not inlined calls to __adEq2 each loop, done to compare 3 char long arrays.


> And have you tried a naive hand-written strComp (just for the sake of completeness) like:

Here it is:

Timings, dmd compiler, best of 4, seconds:
  D #1: 5.72
  D #4: 1.84
  D #5: 1.73
  Psy:  1.59
  D #2: 0.55
  D #3: 0.34


// D version #5
import std.file: read;
import std.c.stdio: printf;

bool cmp2(char[] s1, string s2) {
    if (s1.length != s2.length)
        return false;
    foreach (uint i ; 0 .. s1.length)
        if (s1[i] != s2[i])
            return false;
    return true;
}

int test(char[] data) {
    int count;
    foreach (i; 0 ..  data.length - 3) {
        char[] codon = data[i .. i + 3];
        if (cmp2(codon, "TAG") || cmp2(codon, "TGA") || cmp2(codon, "TAA"))
            count++;
    }
    return count;
}

void main() {
    char[] data0 = cast(char[])read("data.txt");
    int n = 300;
    char[] data = new char[data0.length * n];
    for (size_t pos; pos < data.length; pos += data0.length)
        data[pos .. pos+data0.length] = data0;

    printf("%d\n", test(data));
}


> Also, is there a way to bit-compare given memory areas at much higher speed than element per element (I mean for arrays in general)?

I don't know. I think you can't.

Bye,
bearophile