When I was an intern in the mid-80s we were cross-compiling for a 68000-based device (on a VAX, no less) but had our own version of the C library, supposedly be

When I was an intern in the mid-80s we were cross-compiling for a 68000-based device (on a VAX, no less) but had our own version of the C library, supposedly because of some legal issues with the compiler vendor. Part of this library was the routine to divide 32-bit integers, since the only native divide was 16x16 -> 32. Our implementation was the textbook shift-and-subtract algorithm, which took something like 1000 cycles on that CPU. Our routing algorithm did enough division that this ended up being a big deal, so they asked their intern to optimize it. I came up with a version using the hardware instruction that was maybe 5-10x faster; they tested it a bit and sent a software update out to customers, after which the "phone home" monitoring (using real phone lines and modems in those days) started blowing up. If you divide by zero, naive shift-and-subtract will return MAXINT, while the hardware instruction will raise a divide-by-zero exception. On startup we had a bunch of averages that were default-initialized to zero, and we'd divide by some of them. Getting 32-bit MAXINT wasn't a really big deal - it put a big spike into some moving averages, which decayed pretty quickly. An unexpected exception, though, was a big problem...