;/*
gcc -Wall -o largefmt largefmt.c
quit
*/

/*
** Formatting 64bit numbers with prefix
**
** Written by Harry "Piru" Sintonen <sintonen@iki.fi>
** Public Domain.
**
*/

#define FMT_LITTLE_ENDIAN	0
#define FMT_BIG_ENDIAN		1

/* Set according to CPU byteorder */
#define FMT_BYTE_ORDER		FMT_BIG_ENDIAN

/* 32bit unsigned integer */
typedef unsigned int fmt32_t;

#define HAVE_SNPRINTF

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


int largefmt(unsigned char *buf, size_t len, void *nump);

#if FMT_BYTE_ORDER == FMT_LITTLE_ENDIAN
#define MK64(a,b) {b,a}
#else
#define MK64(a,b) {a,b}
#endif

int main(void)
{
  fmt32_t large[2] = MK64(0x1234567,0x89abcdef);
  //fmt32_t large[2] = MK64(0x1000000,0x89abcdef);
  //fmt32_t large[2] = MK64(0xffffffff,0xffffffff);
  //fmt32_t large[2] = MK64(0x126,0xffffffff);
  //fmt32_t large[2] = MK64(0,0xffff);
  //fmt32_t large[2] = MK64(0,0xfffffff);
  //fmt32_t large[2] = MK64(0,0x3fffffff);
  //fmt32_t large[2] = MK64(0,0x40000000);
  //fmt32_t large[2] = MK64(0,1126);
  unsigned char buf[10];

  largefmt(buf, sizeof(buf), &large);
  printf("%s\n", buf);

  return 0;
}

#if FMT_BYTE_ORDER == FMT_LITTLE_ENDIAN
#  define FMT_LSLI 1
#  define FMT_MSLI 0
#else
#  define FMT_LSLI 0
#  define FMT_MSLI 1
#endif

int largefmt(unsigned char *buf, size_t len, void *nump)
{
  fmt32_t *p = nump;
  fmt32_t val, v, d;
  unsigned char prefix;
#ifndef HAVE_SNPRINTF
  unsigned char tbuf[10]; /* 16383.9PB */
#endif

  /* determine magnitude, and shift accordingly */

  if (p[FMT_LSLI] >= 1024 * 1024 >> 2)
  {
    prefix = 'P';
    val = p[FMT_LSLI] >> (10 - 2);
  }
  else if (p[FMT_LSLI] >= 1024 >> 2)
  {
    prefix = 'T';
    val = (p[FMT_LSLI] << (32 - 30)) | (p[FMT_MSLI] >> 30);
  }
  else if (p[FMT_MSLI] >= 1024 * 1024 * 1024)
  {
    prefix = 'G';
    val = (p[FMT_LSLI] << (32 - 20)) | (p[FMT_MSLI] >> 20);
  }
  else if (p[FMT_MSLI] >= 1024 * 1024)
  {
    prefix = 'M';
    val = p[FMT_MSLI] >> 10;
  }
  else if (p[FMT_MSLI] >= 1024)
  {
    prefix = 'K';
    val = p[FMT_MSLI];
  }
  else
  {
#ifdef HAVE_SNPRINTF
    return snprintf(buf, len, "%uB", p[FMT_MSLI]);
#else
    sprintf(tbuf, "%uB", p[FMT_MSLI]);
    strncpy(buf, tbuf, len);
    return (int) strlen(tbuf); /* really tbuf! */
#endif
  }

  v = val >> 10;
  d = val * 10 >> 10;
  if (d % 10 == 0 && d > v * 10)
  {
    v++;
  }

#ifdef HAVE_SNPRINTF
  return snprintf(buf, len, "%u.%u%cB",
                  v,
                  d % 10,
                  prefix);
#else
  sprintf(tbuf, "%u.%u%cB",
                v,
                d % 10,
                prefix);
  strncpy(buf, tbuf, len);
  return (int) strlen(tbuf); /* really tbuf! */
#endif
}