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Carl Shapiro
cmucl
Commits
28971fe7
Commit
28971fe7
authored
33 years ago
by
wlott
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Added multiplier recoding for ub-32 * ub-32 => ub-32.
parent
9515db88
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compiler/srctran.lisp
+46
-1
46 additions, 1 deletion
compiler/srctran.lisp
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46 additions
and
1 deletion
compiler/srctran.lisp
+
46
−
1
View file @
28971fe7
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@@ -7,7 +7,7 @@
;;; Scott Fahlman or slisp-group@cs.cmu.edu.
;;;
(
ext:file-comment
"$Header: /Volumes/share2/src/cmucl/cvs2git/cvsroot/src/compiler/srctran.lisp,v 1.3
1
1991/11/1
2 16:01:57 ram
Exp $"
)
"$Header: /Volumes/share2/src/cmucl/cvs2git/cvsroot/src/compiler/srctran.lisp,v 1.3
2
1991/11/1
4 05:51:04 wlott
Exp $"
)
;;;
;;; **********************************************************************
;;;
...
...
@@ -930,6 +930,51 @@
`
(
-
(
ash
x
,
len
))
`
(
ash
x
,
len
))))
;;; If both arguments and the result are (unsigned-byte 32), try to come up
;;; with a ``better'' multiplication using multiplier recoding. There are two
;;; different ways the multiplier can be recoded. The more obvious is to shift
;;; X by the correct amount for each bit set in Y and to sum the results. But
;;; if there is a string of bits that are all set, you can add X shifted by
;;; one more then the bit position of the first set bit and subtract X shifted
;;; by the bit position of the last set bit. We can't use this second method
;;; when the high order bit is bit 31 because shifting by 32 doesn't work
;;; too well.
;;;
(
deftransform
*
((
x
y
)
((
unsigned-byte
32
)
(
unsigned-byte
32
))
(
unsigned-byte
32
))
(
unless
(
constant-continuation-p
y
)
(
give-up
))
(
let
((
y
(
continuation-value
y
))
(
result
nil
)
(
first-one
nil
))
(
flet
((
add
(
next-factor
)
(
setf
result
(
if
result
`
(
+
,
next-factor
,
result
)
next-factor
))))
(
declare
(
inline
add
))
(
dotimes
(
bitpos
32
)
(
if
first-one
(
when
(
not
(
logbitp
bitpos
y
))
(
add
(
if
(
=
(
1+
first-one
)
bitpos
)
;; There is only a single bit in the string.
`
(
ash
x
,
first-one
)
;; There are at least two.
`
(
-
(
ash
x
,
bitpos
)
(
ash
x
,
first-one
))))
(
setf
first-one
nil
))
(
when
(
logbitp
bitpos
y
)
(
setf
first-one
bitpos
))))
(
when
first-one
(
cond
((
=
first-one
31
))
((
=
first-one
30
)
(
add
'
(
ash
x
30
)))
(
t
(
add
`
(
-
(
ash
x
31
)
(
ash
x
,
first-one
)))))
(
add
'
(
ash
x
31
))))
(
or
result
0
)))
;;; If arg is a constant power of two, turn floor into a shift and mask.
;;; If ceiling, add in (1- (abs y)) and then do floor.
;;;
...
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