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- /*
- $Id: smult32.c,v 1.1 1996/08/31 12:58:13 aros Exp $
- $Log: smult32.c,v $
- Revision 1.1 1996/08/31 12:58:13 aros
- Merged in/modified for FreeBSD.
-
- Desc:
- Lang: english
- */
- #include "utility_intern.h"
-
- /*****************************************************************************
-
- NAME */
- #include <clib/utility_protos.h>
-
- __AROS_LH2(LONG, SMult32,
-
- /* SYNOPSIS */
- __AROS_LHA(long, arg1, D0),
- __AROS_LHA(long, arg2, D1),
-
- /* LOCATION */
- struct UtilityBase *, UtilityBase, 23, Utility)
-
- /* FUNCTION
- Performs the signed 32-bit multiplication of arg1 * arg2 and
- returns a signed 32 bit value.
-
- INPUTS
- arg1, arg2 - 32 bit signed longs
-
- RESULT
- arg1 * arg2
-
- NOTES
- This can perform the multiplication either using the machines
- native instructions (if they exist), or in software using a
- simple algorithm based on expanding algebraic products.
-
- EXAMPLE
-
- long a = 352543;
- long b = -52464;
- long c = SMult32(a,b);
- c == -1315946768
-
- BUGS
-
- SEE ALSO
- utility/UMult32(), utility/UMult64(), utility/SMult64()
-
- INTERNALS
- We are performing the operation:
-
-
- (2^16 * a + b) * (2^16 * c + d)
- = 2^32 * ab + 2^16 * ad + 2^16 * bc + bd
- = 2^32 * ab + 2^16 ( ad + bc ) + bd
-
- Now since the result is a 32-bit number, the 2^32 term will have
- no effect. (Since 2^32 > max (32-bit number).
-
- Therefore:
- product = 2^16( ad + bc ) + bd
-
- HISTORY
- 29-10-95 digulla automatically created from
- utility_lib.fd and clib/utility_protos.h
- 18-08-96 iaint Implemented as described above.
-
- *****************************************************************************/
- {
- __AROS_FUNC_INIT
-
- #ifdef HAS_32BITMULS
- return arg1 * arg2;
- #else
-
- UWORD a1, b1, a0, b0;
- BOOL neg;
-
- /* Fix everything up so that -ve signs don't vanish */
- if(arg1 < 0)
- {
- neg = 1; arg1 = -arg1;
- }
- else
- neg = 0;
-
- if(arg2 <= 0)
- {
- neg ^= 1; arg2 = -arg2;
- }
-
- a1 = (arg1 >> 16) & 0xffff;
- a0 = arg1 & 0xffff;
- b1 = (arg2 >> 16) & 0xffff;
- b0 = arg2 & 0xffff;
-
- arg1 = (((a0 * b1) + (a1 * b0)) << 16) + (b0 * a0);
- return (neg ? -arg1 : arg1);
- #endif
-
- __AROS_FUNC_EXIT
- } /* SMult32 */
-