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124 lines
3.2 KiB
ArmAsm
124 lines
3.2 KiB
ArmAsm
/*
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* Signed multiply, from Appendix E of the Sparc Version 8
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* Architecture Manual.
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*/
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/*
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* Returns %o0 * %o1 in %o1%o0 (i.e., %o1 holds the upper 32 bits of
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* the 64-bit product).
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*
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* This code optimizes short (less than 13-bit) multiplies.
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*/
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#include "DEFS.h"
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FUNC(.mul)
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mov %o0, %y ! multiplier -> Y
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andncc %o0, 0xfff, %g0 ! test bits 12..31
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be Lmul_shortway ! if zero, can do it the short way
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andcc %g0, %g0, %o4 ! zero the partial product and clear N and V
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/*
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* Long multiply. 32 steps, followed by a final shift step.
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*/
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mulscc %o4, %o1, %o4 ! 1
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mulscc %o4, %o1, %o4 ! 2
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mulscc %o4, %o1, %o4 ! 3
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mulscc %o4, %o1, %o4 ! 4
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mulscc %o4, %o1, %o4 ! 5
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mulscc %o4, %o1, %o4 ! 6
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mulscc %o4, %o1, %o4 ! 7
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mulscc %o4, %o1, %o4 ! 8
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mulscc %o4, %o1, %o4 ! 9
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mulscc %o4, %o1, %o4 ! 10
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mulscc %o4, %o1, %o4 ! 11
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mulscc %o4, %o1, %o4 ! 12
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mulscc %o4, %o1, %o4 ! 13
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mulscc %o4, %o1, %o4 ! 14
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mulscc %o4, %o1, %o4 ! 15
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mulscc %o4, %o1, %o4 ! 16
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mulscc %o4, %o1, %o4 ! 17
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mulscc %o4, %o1, %o4 ! 18
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mulscc %o4, %o1, %o4 ! 19
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mulscc %o4, %o1, %o4 ! 20
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mulscc %o4, %o1, %o4 ! 21
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mulscc %o4, %o1, %o4 ! 22
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mulscc %o4, %o1, %o4 ! 23
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mulscc %o4, %o1, %o4 ! 24
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mulscc %o4, %o1, %o4 ! 25
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mulscc %o4, %o1, %o4 ! 26
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mulscc %o4, %o1, %o4 ! 27
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mulscc %o4, %o1, %o4 ! 28
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mulscc %o4, %o1, %o4 ! 29
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mulscc %o4, %o1, %o4 ! 30
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mulscc %o4, %o1, %o4 ! 31
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mulscc %o4, %o1, %o4 ! 32
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mulscc %o4, %g0, %o4 ! final shift
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! If %o0 was negative, the result is
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! (%o0 * %o1) + (%o1 << 32))
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! We fix that here.
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#if 0
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tst %o0
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bge 1f
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rd %y, %o0
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! %o0 was indeed negative; fix upper 32 bits of result by subtracting
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! %o1 (i.e., return %o4 - %o1 in %o1).
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retl
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sub %o4, %o1, %o1
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1:
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retl
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mov %o4, %o1
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#else
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/* Faster code adapted from tege@sics.se's code for umul.S. */
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sra %o0, 31, %o2 ! make mask from sign bit
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and %o1, %o2, %o2 ! %o2 = 0 or %o1, depending on sign of %o0
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rd %y, %o0 ! get lower half of product
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retl
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sub %o4, %o2, %o1 ! subtract compensation
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! and put upper half in place
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#endif
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Lmul_shortway:
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/*
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* Short multiply. 12 steps, followed by a final shift step.
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* The resulting bits are off by 12 and (32-12) = 20 bit positions,
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* but there is no problem with %o0 being negative (unlike above).
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*/
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mulscc %o4, %o1, %o4 ! 1
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mulscc %o4, %o1, %o4 ! 2
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mulscc %o4, %o1, %o4 ! 3
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mulscc %o4, %o1, %o4 ! 4
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mulscc %o4, %o1, %o4 ! 5
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mulscc %o4, %o1, %o4 ! 6
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mulscc %o4, %o1, %o4 ! 7
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mulscc %o4, %o1, %o4 ! 8
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mulscc %o4, %o1, %o4 ! 9
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mulscc %o4, %o1, %o4 ! 10
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mulscc %o4, %o1, %o4 ! 11
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mulscc %o4, %o1, %o4 ! 12
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mulscc %o4, %g0, %o4 ! final shift
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/*
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* %o4 has 20 of the bits that should be in the low part of the
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* result; %y has the bottom 12 (as %y's top 12). That is:
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*
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* %o4 %y
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* +----------------+----------------+
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* | -12- | -20- | -12- | -20- |
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* +------(---------+------)---------+
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* --hi-- ----low-part----
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*
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* The upper 12 bits of %o4 should be sign-extended to form the
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* high part of the product (i.e., highpart = %o4 >> 20).
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*/
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rd %y, %o5
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sll %o4, 12, %o0 ! shift middle bits left 12
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srl %o5, 20, %o5 ! shift low bits right 20, zero fill at left
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or %o5, %o0, %o0 ! construct low part of result
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retl
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sra %o4, 20, %o1 ! ... and extract high part of result
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