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/*
############################################################################
#
# File: pack.c
#
# Subject: Functions to pack and unpack binary data
#
# Author: Gregg M. Townsend
#
# Date: November 17, 1997
#
############################################################################
#
# This file is in the public domain.
#
############################################################################
#
# s := pack(value, flags, width)
# x := unpack(string, flags)
#
# Flag characters are as follows:
#
# l -- little-endian [default]
# b -- big-endian
# n -- host platform's native packing order
#
# i -- integer [default]
# u -- unsigned integer
# r -- real (host platform's native float or double format)
#
# The default width is 4.
#
# Integer values must fit in a standard Icon integer (not large integer).
# Consequently, a word-sized value cannot have the high bit set if unsigned.
# Floating values can only be converted to/from a string width matching
# sizeof(float) or sizeof(double).
#
# Size/type combinations that can't be handled produce errors.
# Valid combinations produce failure if the value overflows.
#
# Some of this code assumes a twos-complement architecture with 8-bit bytes.
#
############################################################################
#
# Requires: Dynamic loading
#
############################################################################
*/
#include "icall.h"
#include <string.h>
#define F_LTL 0x100 /* little-endian */
#define F_BIG 0x200 /* big-endian */
#define F_REV 0x400 /* internal flag: reversal needed */
#define F_INT 1 /* integer */
#define F_UNS 2 /* unsigned integer */
#define F_REAL 4 /* real */
#define DEF_WIDTH 4 /* default width */
#define MAX_WIDTH 256 /* maximum width */
static unsigned long testval = 1;
#define LNATIVE (*(char*)&testval) /* true if machine is little-endian */
static int flags(char *s, int n);
static void *memrev(void *s1, void *s2, size_t n);
/*
* pack(value, flags, width)
*/
int pack(int argc, descriptor argv[]) /*: pack integer into bytes */
{
int f, i, n, x;
long v;
unsigned char *s, obuf[MAX_WIDTH];
union { float f; double d; unsigned char buf[MAX_WIDTH]; } u;
/*
* check arguments
*/
if (argc == 0)
Error(102); /* no value given */
if (argc > 1) {
ArgString(2);
if ((f = flags(StringAddr(argv[2]), StringLen(argv[2]))) == 0)
ArgError(2, 205); /* illegal flag string */
}
else
f = flags("", 0);
if (argc > 2) {
ArgInteger(3);
n = IntegerVal(argv[3]);
if (n < 0 || n > MAX_WIDTH)
ArgError(3, 205); /* too long to handle */
}
else
n = DEF_WIDTH;
if (f & F_REAL) {
/*
* pack real value
*/
ArgReal(1);
if (n == sizeof(double))
u.d = RealVal(argv[1]);
else if (n == sizeof(float))
u.f = RealVal(argv[1]);
else
ArgError(3, 205); /* illegal length for real value */
if (f & F_REV)
RetStringN(memrev(obuf, u.buf, n), n);
else
RetStringN((char *)u.buf, n);
}
/*
* pack integer value
*/
ArgInteger(1);
v = IntegerVal(argv[1]); /* value */
if (v >= 0)
x = 0; /* sign extension byte */
else if (f & F_UNS)
Fail; /* invalid unsigned value */
else
x = (unsigned char) -1;
for (s = obuf, i = 0; i < sizeof(long); i++) {
*s++ = v & 0xFF; /* save in little-endian fashion */
v = ((unsigned long)v) >> 8;
}
while (i++ < n)
*s++ = x; /* extend if > sizeof(long) */
for (i = n; i < sizeof(long); i++) /* check that all bits did fit */
if (obuf[i] != x)
Fail; /* overflow */
if (f & F_BIG)
RetStringN(memrev(u.buf, obuf, n), n);
else
RetStringN((char *)obuf, n);
}
/*
* unpack(string, flags)
*/
int unpack(int argc, descriptor argv[]) /*: unpack integer from bytes */
{
int f, i, n, x;
long v;
unsigned char *s;
union { float f; double d; unsigned char buf[MAX_WIDTH]; } u;
/*
* check arguments
*/
ArgString(1);
s = (unsigned char *)StringAddr(argv[1]);
n = StringLen(argv[1]);
if (n > MAX_WIDTH)
ArgError(1, 205); /* too long to handle */
if (argc > 1) {
ArgString(2);
if ((f = flags(StringAddr(argv[2]), StringLen(argv[2]))) == 0)
ArgError(2, 205); /* illegal flag string */
}
else
f = flags("", 0);
if (f & F_REAL) {
/*
* unpack real value
*/
if (f & F_REV)
memrev(u.buf, s, n);
else
memcpy(u.buf, s, n);
if (n == sizeof(double))
RetReal(u.d);
else if (n == sizeof(float))
RetReal(u.f);
else
ArgError(1, 205); /* illegal length for real value */
}
/*
* unpack integer value
*/
if (f & F_BIG)
s = memrev(u.buf, s, n); /* put in little-endian order */
for (v = i = 0; i < n && i < sizeof(long); i++)
v |= *s++ << (8 * i); /* pack into a long */
if (v >= 0)
x = 0; /* sign extension byte */
else if (f & F_UNS)
Fail; /* value overflows as unsigned */
else
x = (unsigned char) -1;
for (; i < n; i++) /* check bytes beyond sizeof(long) */
if (*s++ != x)
Fail; /* value overflows a long */
RetInteger(v); /* return value */
}
/*
* flags(addr, len) -- interpret flag string, return 0 if error
*/
static int flags(char *s, int n)
{
int f = 0;
while (n--) switch(*s++) {
case 'l': f |= F_LTL; break;
case 'b': f |= F_BIG; break;
case 'n': f |= (LNATIVE ? F_LTL : F_BIG); break;
case 'i': f |= F_INT; break;
case 'u': f |= F_UNS + F_INT; break;
case 'r': f |= F_REAL; break;
default: return 0;
}
if (((f & F_LTL) && (f & F_BIG)) | ((f & F_INT) && (f & F_REAL)))
return 0; /* illegal conflict */
if (!(f & F_BIG))
f |= F_LTL; /* default packing is little-endian */
if (!(f & F_REAL))
f |= F_INT; /* default type is integer */
if (f & (LNATIVE ? F_BIG : F_LTL))
f |= F_REV; /* set flag if non-native mode */
return f;
}
/*
* memrev(s1, s2, n) -- copy reversal of s2 into s1, returning s1
*/
static void *memrev(void *s1, void *s2, size_t n)
{
unsigned char *c1 = s1;
unsigned char *c2 = (unsigned char *)s2 + n;
while (n-- > 0)
*c1++ = *--c2;
return s1;
}
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