1/* $Id: mul.S,v 1.1.1.1 2007/08/03 18:52:17 Exp $
2 * mul.S:       This routine was taken from glibc-1.09 and is covered
3 *              by the GNU Library General Public License Version 2.
4 */
5
6/*
7 * Signed multiply, from Appendix E of the Sparc Version 8
8 * Architecture Manual.
9 */
10
11/*
12 * Returns %o0 * %o1 in %o1%o0 (i.e., %o1 holds the upper 32 bits of
13 * the 64-bit product).
14 *
15 * This code optimizes short (less than 13-bit) multiplies.
16 */
17
18	.globl .mul
19	.globl _Mul
20.mul:
21_Mul:	/* needed for export */
22	mov	%o0, %y		! multiplier -> Y
23	andncc	%o0, 0xfff, %g0	! test bits 12..31
24	be	Lmul_shortway	! if zero, can do it the short way
25	 andcc	%g0, %g0, %o4	! zero the partial product and clear N and V
26
27	/*
28	 * Long multiply.  32 steps, followed by a final shift step.
29	 */
30	mulscc	%o4, %o1, %o4	! 1
31	mulscc	%o4, %o1, %o4	! 2
32	mulscc	%o4, %o1, %o4	! 3
33	mulscc	%o4, %o1, %o4	! 4
34	mulscc	%o4, %o1, %o4	! 5
35	mulscc	%o4, %o1, %o4	! 6
36	mulscc	%o4, %o1, %o4	! 7
37	mulscc	%o4, %o1, %o4	! 8
38	mulscc	%o4, %o1, %o4	! 9
39	mulscc	%o4, %o1, %o4	! 10
40	mulscc	%o4, %o1, %o4	! 11
41	mulscc	%o4, %o1, %o4	! 12
42	mulscc	%o4, %o1, %o4	! 13
43	mulscc	%o4, %o1, %o4	! 14
44	mulscc	%o4, %o1, %o4	! 15
45	mulscc	%o4, %o1, %o4	! 16
46	mulscc	%o4, %o1, %o4	! 17
47	mulscc	%o4, %o1, %o4	! 18
48	mulscc	%o4, %o1, %o4	! 19
49	mulscc	%o4, %o1, %o4	! 20
50	mulscc	%o4, %o1, %o4	! 21
51	mulscc	%o4, %o1, %o4	! 22
52	mulscc	%o4, %o1, %o4	! 23
53	mulscc	%o4, %o1, %o4	! 24
54	mulscc	%o4, %o1, %o4	! 25
55	mulscc	%o4, %o1, %o4	! 26
56	mulscc	%o4, %o1, %o4	! 27
57	mulscc	%o4, %o1, %o4	! 28
58	mulscc	%o4, %o1, %o4	! 29
59	mulscc	%o4, %o1, %o4	! 30
60	mulscc	%o4, %o1, %o4	! 31
61	mulscc	%o4, %o1, %o4	! 32
62	mulscc	%o4, %g0, %o4	! final shift
63
64	! If %o0 was negative, the result is
65	!	(%o0 * %o1) + (%o1 << 32))
66	! We fix that here.
67
68	/* Faster code adapted from tege@sics.se's code for umul.S.  */
69	sra	%o0, 31, %o2	! make mask from sign bit
70	and	%o1, %o2, %o2	! %o2 = 0 or %o1, depending on sign of %o0
71	rd	%y, %o0		! get lower half of product
72	retl
73	 sub	%o4, %o2, %o1	! subtract compensation
74				!  and put upper half in place
75
76Lmul_shortway:
77	/*
78	 * Short multiply.  12 steps, followed by a final shift step.
79	 * The resulting bits are off by 12 and (32-12) = 20 bit positions,
80	 * but there is no problem with %o0 being negative (unlike above).
81	 */
82	mulscc	%o4, %o1, %o4	! 1
83	mulscc	%o4, %o1, %o4	! 2
84	mulscc	%o4, %o1, %o4	! 3
85	mulscc	%o4, %o1, %o4	! 4
86	mulscc	%o4, %o1, %o4	! 5
87	mulscc	%o4, %o1, %o4	! 6
88	mulscc	%o4, %o1, %o4	! 7
89	mulscc	%o4, %o1, %o4	! 8
90	mulscc	%o4, %o1, %o4	! 9
91	mulscc	%o4, %o1, %o4	! 10
92	mulscc	%o4, %o1, %o4	! 11
93	mulscc	%o4, %o1, %o4	! 12
94	mulscc	%o4, %g0, %o4	! final shift
95
96	/*
97	 *  %o4 has 20 of the bits that should be in the low part of the
98	 * result; %y has the bottom 12 (as %y's top 12).  That is:
99	 *
100	 *	  %o4		    %y
101	 * +----------------+----------------+
102	 * | -12- |   -20-  | -12- |   -20-  |
103	 * +------(---------+------)---------+
104	 *  --hi-- ----low-part----
105	 *
106	 * The upper 12 bits of %o4 should be sign-extended to form the
107	 * high part of the product (i.e., highpart = %o4 >> 20).
108	 */
109
110	rd	%y, %o5
111	sll	%o4, 12, %o0	! shift middle bits left 12
112	srl	%o5, 20, %o5	! shift low bits right 20, zero fill at left
113	or	%o5, %o0, %o0	! construct low part of result
114	retl
115	 sra	%o4, 20, %o1	! ... and extract high part of result
116
117	.globl	.mul_patch
118.mul_patch:
119	smul	%o0, %o1, %o0
120	retl
121	 rd	%y, %o1
122	nop
123