SPRUI30H November 2015 – May 2024 DRA745 , DRA746 , DRA750 , DRA756
Left Most Bit Detection
LMBD ucst3, src2, dst
Functional unit = L
32 bit
31 | 30 | 29 | 28 | 27 | 26 | 25 | 24 | 23 | 22 | 21 | 20 | 19 | 18 | 16 | 15 | 13 | 12 | 10 | 9 | 0 |
x | x | x | x | x | x | x | x | x | x | x | x | x | ucst3 | dst | src2 | 1 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 1 |
3 | 3 | 3 | opcode |
The LSB of ucst3 determines whether to search for a leftmost 1 or 0 in src2. The number of bits to the left of the first 1 or 0 when searching for a 1 or 0, respectively, is placed in dst.
The following diagrams illustrate the operation of LMBD for several cases.
When searching for 0 in src2, LMBD returns 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 |
0 | 1 | x | x | x | x | x | x | x | x | x | x | x | x | x | x | x | x | x | x | x | x | x | x | x | x | x | x | x | x | x | x |
When searching for 1 in src2, LMBD returns 4:
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 |
0 | 0 | 0 | 0 | 1 | x | x | x | x | x | x | x | x | x | x | x | x | x | x | x | x | x | x | x | x | x | x | x | x | x | x | x |
When searching for 0 in src2, LMBD returns 32:
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 |
1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |
CSR:EQ = (dst == 0)
dst = if (ucst3 == 0), lmb0(src2)
dst = if (ucst3 == 1), lmb1(src2)