AE_LBSI — signed bitstream lookahead, returning 1 to 16 bits based on immediate

Instruction Word

Slot
Inst
6
3
6
2
6
1
6
0
5
9
5
8
5
7
5
6
5
5
5
4
5
3
5
2
5
1
5
0
4
9
4
8
4
7
4
6
4
5
4
4
4
3
4
2
4
1
4
0
3
9
3
8
3
7
3
6
3
5
3
4
3
3
3
2
3
1
3
0
2
9
2
8
2
7
2
6
2
5
2
4
2
3
2
2
2
1
2
0
1
9
1
8
1
7
1
6
1
5
1
4
1
3
1
2
1
1
1
0
9876543210
Format x24 - 24 bit(s) 0
AE_LBSI 01101001 0111 0100
r 3210
ae_fld_fhba4 3210

Assembler Syntax

AE_LBSI a0..15(arr), 1..16

C Syntax

#include <xtensa/tie/xt_hifi2.h>

extern int AE_LBSI(immediate ba);

Description

AE_LBSI is a look ahead in the bit stream. Returns as few as 1 bit or as many as 16 bits from the head of the bit stream. The number of bits to return is given by the immediate value i, and must lie in the range [1..16]. No state is updated; this is a lookahead instruction. The bits from the bit stream are returned sign-extended, right-justified in a.

Implementation Pipeline

In Out
AE_BITPTR Mstage, AE_BITHEAD Mstage arr Mstage

Protos that use AE_LBSI

proto AE_LBSI { out int32 a, in immediate ba }{}{
AE_LBSI a, ba + 0;
}