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EXTU Extract and Zero-Extend a Bit Field
3-114 Instruction Set SPRU733
Description The field in src2, specified by csta and cstb, is extracted and zero extended
to 32 bits. The extract is performed by a shift left followed by an unsigned shift
right. csta and cstb are the amounts to shift left and shift right, respectively.
This can be thought of in terms of the LSB and MSB of the field to be extracted.
Then csta = 31 − MSB of the field and cstb = csta + LSB of the field. The shift
left and shift right amounts may also be specified as the ten LSBs of the src1
register with cstb being bits 0−4 and csta bits 5−9. In the example below, csta
is 12 and cstb is 11 + 12 = 23. Only the ten LSBs are valid for the register
version of the instruction. If any of the 22 MSBs are non-zero, the result is
invalid.
0 1010011010000000000000000000000
x
csta
cstb − cst a
xxxxxxxx 1101xxxxxxxxxxxxx 010x10
src2
dst
xxx0000011 1110 0 0 xxxxxxxx 00000000
Shifts left by 12 to produce:
Then shifts right by 23 to produce:
1)
2)
3)
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Execution If the constant form is used:
if (cond) src2 extu csta, cstb
→ dst
else nop
If the register width and offset form is used:
if (cond) src2 extu src1
9..5
, src1
4..0
→ dst
else nop
Pipeline
Stage
E1
Read src1, src2
Written dst
Unit in use
.S
Pipeline