> and this sped it up by 100% Over 1,000%. x87 fsqrt took ~70 cycles on the Pentium MMX x87, x87 fdiv was ~39 cycles - so doing inverse square root on x87 was

> and this sped it up by 100% Over 1,000%. x87 fsqrt took ~70 cycles on the Pentium MMX x87, x87 fdiv was ~39 cycles - so doing inverse square root on x87 was ~109 cycles. The fast inverse square root routine was in the vicinity of 10 cycles. In Quake, each vertex needed to have its normal vector calculated, which resulted in... I dunno, 100,000 inverse square root calculations per second, assuming you're pushing 100,000 polygons per second. Assuming a 100MHz CPU, the x87 inverse square root calculations would consume 11% of the CPU cycles, the fast inverse square root routine would consume 1% of the CPU cycles. https://en.wikipedia.org/wiki/X87#Performance https://en.wikipedia.org/wiki/X87#Performance