![](http://datasheet.mmic.net.cn/260000/PTM1300FBEA_datasheet_15959396/PTM1300FBEA_313.png)
Philips Semiconductors
DSPCPU Operations for TM1300
PRODUCT SPECIFICATION
A-27
Dual clipped subtract of signed 16-bit halfwords
SYNTAX
[ IF rguard ] dspidualsub rsrc1 rsrc2
→
rdest
FUNCTION
if
rguard
then {
temp1
←
sign_ext16to32(rsrc1<15:0>) – sign_ext16to32(rsrc2<15:0>)
temp2
←
sign_ext16to32(rsrc1<31:16>) – sign_ext16to32(rsrc2<31:16>)
if
temp1 < 0xffff8000
then
temp1
←
0x8000
if
temp2 < 0xffff8000
then
temp2
←
0x8000
if
temp1 > 0x7fff
then
temp1
←
0x7fff
if
temp2 > 0x7fff
then
temp2
←
0x7fff
rdest<31:16>
←
temp2<15:0>
rdest<15:0>
←
temp1<15:0>
}
ATTRIBUTES
Function unit
Operation code
Number of operands
Modifier
Modifier range
Latency
Issue slots
dspalu
71
2
No
—
2
1, 3
DESCRIPTION
As shown below, the
dspidualsub
operation computes two 16-bit clipped, signed differences separately on the
two pairs of high and low 16-bit halfwords of rsrc1 and rsrc2 Both differences are clipped into the range [2
15
–1..–2
15
]
(or [0x7fff..0x8000]) and written into the corresponding halfwords of rdest All values are signed 16-bit integers.
The
dspidualsub
operation optionally takes a guard, specified in rguard If a guard is present, its LSB controls the
modification of the destination register. If the LSB of rguardis 1, rdestis written; otherwise, rdestis not changed.
EXAMPLES
Initial Values
Operation
Result
r30 = 0x12340032, r40 = 0x00010002
r10 = 0, r30 = 0x12340032, r40 = 0x00010002
dspidualsub r30 r40
→
r60
IF r10 dspidualsub r30 r40
→
r70
r60
←
0x12330030
no change, since guard is
false
r100
←
0x12330030
r90
←
0x80007fff
r125
←
0x7fff8000
r20 = 1, r30 = 0x12340032, r40 = 0x00010002
r50 = 0x80000001, r80 = 0x00018001
r110 = 0x00018001, r120 = 0x80010002
IF r20 dspidualsub r30 r40
→
r100
dspidualsub r50 r80
→
r90
dspidualsub r110 r120
→
r125
0
1
3
rsrc1
0
1
3
rsrc2
0
3
rdest
1
0
1
0
1
Two full-precision
17-bit signed differences
Clip to [2
15
–1..–2
15
]
Clip to [2
15
–1..–2
15
]
signed
signed
signed
signed
signed
signed
signed
signed
SEE ALSO
dspidualabs dspidualadd
dspidualmul dspiabs
dspidualsub