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From: Tim Rentsch <tr.17687@z991.linuxsc.com>
Newsgroups: comp.lang.c
Subject: Re: Sort of trivial code challenge - may be interesting to you anyway
Date: Sat, 07 Mar 2026 12:02:11 -0800
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Xref: csiph.com comp.lang.c:396851

Lew Pitcher <lew.pitcher@digitalfreehold.ca> writes:

> [...] I look forward to seeing /your/ code :-)

Here we go...

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <setjmp.h>

typedef size_t  Z;
typedef _Bool   B;

static  Z       k,  h,  w,  c;
static  int     d;
static  jmp_buf jb;

#define GO(x)         longjmp( jb, x )
#define NUMBERISH(p)  ((p) && *(p) && (p)[ strspn((p),"0123456789") ] == 0)

enum {
  START,         // the initial state; must be zero
    AFU, USAGE,  // give suitable message and exit
    ROOT, DRAT,  // find ceiling( sqrt( cutoff ) ); possible no joy exit
    HWC,         // display H*W values with cutoff C
  FIN,           // exit program
};

int
main( int argc, char *argv[] ){
 switch(  setjmp( jb )  ){
  case START: {
     B usage   =  argc < 2 || argc > 4;

     B g1      =  argc > 1  &&  NUMBERISH( argv[1] );
     B g2      =  argc > 2  &&  NUMBERISH( argv[2] );
     B g3      =  argc > 3  &&  NUMBERISH( argv[3] );

     Z a1      =  g1 ? strtoul( argv[1], 0, 10 ) : 0;
     Z a2      =  g2 ? strtoul( argv[2], 0, 10 ) : 0;
     Z a3      =  g3 ? strtoul( argv[3], 0, 10 ) : 0;

     B square  =  argc == 2 &&  g1;
     B hw      =  argc == 3 &&  g1&&g2 && a1&&a2;
     B hwc     =  argc == 4 &&  g1&&g2 && a1&&a2 && g3;

     k = 0;
     h = hw || hwc ? a1  :  a1/4 + !a1;  // note: initial value(h) > 0
     w = hw || hwc ? a2  :  h;
     c = square ? a1  :  !hwc ? h*w  :  a3 > h*w ? h*w  :  a3;
     d = snprintf( 0, 0, "%zu", c );

     GO( usage ?USAGE : square ?ROOT : (hw||hwc) && a1&&a2 ?HWC : AFU );
  }

  case AFU:
     printf( " urk... bad arguments\n" );
     GO( USAGE );

  case USAGE:
     printf( " usage:\n" );
     printf( "     %s cutoff  {{for square}}\n", argv[0] );
     printf( "     %s rows columns [cutoff]\n",  argv[0] );
     GO( FIN );

  case ROOT: {
     h =  c < 2 ? 1  :  c < 5 ? 2  :  (h + c/h) / 2;
     h += h*h < c;
     w = h;
     B done  =  c < 2  ||  h*h < c+2*h && c <= h*h;
     B good  =  c < 2  ||  h*h < c+h   && c <= h*h;
     GO(  !done ?ROOT  :  good ?HWC  :  DRAT  );
  }

  case DRAT:
     printf( " square with cutoff %zu - no joy\n", c );
     GO( FIN );

  case HWC: {
     B eol    =  k/h + 1 == w;
     B end    =  k+1 + (h>c ? h-c : 0) >= h*w;
     Z nextk  =  eol ? k - (w-1)*h + 1 : k+h;

     printf(  k < c        ? " %*zu" : "",  d,  k+1 );
     printf(  c > 0 && eol ? "\n"    : ""           );

     GO(  end ?(printf( "------\n" ), FIN)  :  (k = nextk, HWC)  );
  }
 }
}