ref: 12c8e27a761f7bb673e1c94f5f3e3b9807bf99a6
dir: /sys/src/ape/lib/ap/math/floor.c/
#include <math.h> /* * floor and ceil-- greatest integer <= arg * (resp least >=) */ double floor(double d) { double fract; if(d < 0) { fract = modf(-d, &d); if(fract != 0.0) d += 1; d = -d; } else modf(d, &d); return d; } double ceil(double d) { return -floor(-d); }