Include/longintrepr.h

/***********************************************************
Copyright 1991, 1992 by Stichting Mathematisch Centrum, Amsterdam, The
Netherlands.

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/* This is published for the benefit of "friend" marshal.c only. */

/* Parameters of the long integer representation.
   These shouldn't have to be changed as C should guarantee that a short
   contains at least 16 bits, but it's made changeable any way.
   Note: 'digit' should be able to hold 2*MASK+1, and 'twodigits'
   should be able to hold the intermediate results in 'mul'
   (at most MASK << SHIFT).
   Also, x_sub assumes that 'digit' is an unsigned type, and overflow
   is handled by taking the result mod 2**N for some N > SHIFT.
   And, at some places it is assumed that MASK fits in an int, as well. */

typedef unsigned short digit;
typedef unsigned int wdigit; /* digit widened to parameter size */
typedef unsigned long twodigits;
typedef long stwodigits; /* signed variant of twodigits */

#define SHIFT	15
#define BASE	((digit)1 << SHIFT)
#define MASK	((int)(BASE - 1))

/* Long integer representation.
   The absolute value of a number is equal to
   	SUM(for i=0 through abs(ob_size)-1) ob_digit[i] * 2**(SHIFT*i)
   Negative numbers are represented with ob_size < 0;
   zero is represented by ob_size == 0.
   In a normalized number, ob_digit[abs(ob_size)-1] (the most significant
   digit) is never zero.  Also, in all cases, for all valid i,
   	0 <= ob_digit[i] <= MASK.
   The allocation fuction takes care of allocating extra memory
   so that ob_digit[0] ... ob_digit[abs(ob_size)-1] are actually available. */

struct _longobject {
	OB_HEAD
	int ob_size; /* XXX Hack! newvarobj() stores it as unsigned! */
	digit ob_digit[1];
};

longobject *alloclongobject PROTO((int));