2 ms·

OK, I just tested with gcc 4.6.0, and unless I've screwed something up, it looks like (at -O4) it actually optimizes these into the exact same code. As in the

• apaprocki 15y ago
  Since you showed interest, using this as the for loop tweaks it even a bit more :) /* temp number */ char tmp[20]; int pos = 0; int j = i > 0 ? i : -i; do { tmp[pos++] = '0' + j % 10; j /= 10; } while (j != 0 && pos <= 20); /* output both numbers simultaneously */ char x[44], *p1 = x, *p2 = x + 1 + pos; if (i < 0) { *p1++ = '-'; *p2++ = '-'; } do { int tpos = --pos; *p1++ = tmp[tpos]; *p2++ = tmp[tpos]; } while (pos > 0); *p1 = ' '; *p2 = '\0';
  • 1amzave 15y ago
    Well, if you really want to go apples-to-oranges and specialize as much as possible for the sequentially increasing case we're dealing with here, you could just do your arithmetic directly on the ASCII string itself, complete with a little ripple-carry loop...I bet that'd be fast. If I'm remembering correctly, I think x86 actually has dedicated instructions for ASCII arithmetic (though they're probably so unoptimized in a modern microarchitecture it'd probably be faster to avoid them).