This week I learned...

It's prehistory week at the jorendorff household. This week I learned:

• The fossilized skeletons of a 14-foot Xiphactinus (a mean-looking Late Cretaceous fish) and its last meal, a merely 6-foot bony fish which it swallowed whole, are on display at the Sternberg Museum of Natural History in Hays, Kansas.

• Woolly mammoths had a three-inch-thick layer of fat underneath thick skin, fur, and long shaggy hair. (Yet their environment was such that occasionally one would be flash-frozen, without spoiling the meat, to be eaten by modern dogs ten thousand years later.)

Last week:

• The original Nintendo GameBoy had an 8-bit processor with a HALT instruction which games were supposed to use to wait for interrupts. At least one game would sometimes busy-wait instead (yuck!).

• There's a tool, dwarfdump, that dumps DWARF debug info from an executable or object file.

• On Mac there's a lazy debug-info-linking scheme that causes dwarfdump not to see any DWARF in compiled executables. The Mac tools that come with Xcode are aware of this magic, but dwarfdump isn't.

Earlier still:

• The Spiral of Theodorus shows that the square roots of integers can be constructed with straight edge and compass.

• According to Tim Sweeney, quoted in this DDJ article:

  Any loop written in a traditional programming language can be vectorized, to execute 16 iterations of the loop in parallel on Larrabee vector units, provided the loop body meets the following criteria:

  • Its call graph is statically known.
  • There are no data dependencies between iterations.

  So compilers will be able to do a lot more vectorization.