ref: 97f4b9b97c470501d25ac82cad771bdff75e9b59
dir: /sqrt.c/
#include <u.h> #include <libc.h> int iters; /* * Heron's method to compute the √ * * iteratively do * x1 = ½(x0 + n/x0) * since * lim M→∞ (xM) = √n */ //double //√(double n) //{ // int i; // double x; // // x = 2; // for(i = 0; i < iters; i++) // x = 0.5*(x + n/x); // return x; //} double √(double n) { double x0, x; if(n == 0) return 0; x0 = -1; x = n > 1? n/2: 1; while(x0 != x){ x0 = x; x = 0.5*(x0 + n/x0); iters++; } return x; } void usage(void) { fprint(2, "usage: %s number [prec]\n", argv0); exits("usage"); } void main(int argc, char *argv[]) { int prec; double n; prec = 10; ARGBEGIN{ default: usage(); }ARGEND if(argc < 1) usage(); n = strtod(argv[0], nil); if(n < 0) sysfatal("too complex"); if(argc > 2) prec = strtoul(argv[1], nil, 10); print("√%g = %.*f (took %d iterations)\n", n, prec, √(n), iters); exits(nil); }