AE_LBK — bitstream lookahead, return bits based on AR register (keeping low bits of another AR)

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_LBK 10000011 0100
r 3210
s 3210
t 3210

Assembler Syntax

AE_LBK a0..15(arr), a0..15(ars), a0..15(art)

C Syntax

#include <xtensa/tie/xt_hifi2.h>

extern unsigned AE_LBK(unsigned a0, unsigned ba);

Description

AE_LBK is a look ahead in the bit stream, keeping low bits of a0. Return as few as 0 bits or as many as 16 bits from the head of the bit stream in the low bits of a, with the remaining bits of a filled with low bits from a0. The number of bits to move from the stream to a is given by the low five bits of a1, and must lie in the range [0..16]. No state is updated; this is a lookahead instruction.

Implementation Pipeline

In Out
AE_BITPTR Mstage, AE_BITHEAD Mstage, ars Mstage, art Mstage arr Mstage

Protos that use AE_LBK

proto AE_LBK { out uint32 a, in uint32 a0, in uint32 ba }{}{
AE_LBK a, a0, ba;
}