strntoumax.c

/*
 * strntoumax.c
 *
 * The strntoumax() function and associated
 */

#include <stddef.h>
#include <stdint.h>
#include <ctype.h>

static inline int digitval(int ch)
{
  if ( ch >= '0' && ch <= '9' ) {
    return ch-'0';
  } else if ( ch >= 'A' && ch <= 'Z' ) {
    return ch-'A'+10;
  } else if ( ch >= 'a' && ch <= 'z' ) {
    return ch-'a'+10;
  } else {
    return -1;
  }
}

uintmax_t strntoumax(const char *nptr, char **endptr, int base, size_t n)
{
  int minus = 0;
  uintmax_t v = 0;
  int d;

  while ( n && isspace((unsigned char)*nptr) ) {
    nptr++;
    n--;
  }

  /* Single optional + or - */
  if ( n && *nptr == '-' ) {
    minus = 1;
    nptr++;
    n--;
  } else if ( n && *nptr == '+' ) {
    nptr++;
  }

  if ( base == 0 ) {
    if ( n >= 2 && nptr[0] == '0' &&
	 (nptr[1] == 'x' || nptr[1] == 'X') ) {
      n -= 2;
      nptr += 2;
      base = 16;
    } else if ( n >= 1 && nptr[0] == '0' ) {
      n--;
      nptr++;
      base = 8;
    } else {
      base = 10;
    }
  } else if ( base == 16 ) {
    if ( n >= 2 && nptr[0] == '0' &&
	 (nptr[1] == 'x' || nptr[1] == 'X') ) {
      n -= 2;
      nptr += 2;
    }
  }

  while ( n && (d = digitval(*nptr)) >= 0 && d < base ) {
    v = v*base + d;
    n--;
    nptr++;
  }

  if ( endptr )
    *endptr = (char *)nptr;

  return minus ? -v : v;
}