<!---======================= begin_copyright_notice ============================

Copyright (C) 2020-2021 Intel Corporation

SPDX-License-Identifier: MIT

============================= end_copyright_notice ==========================-->

 

## Opcode

  FBH = 0x2f

## Format

| | | | |
| --- | --- | --- | --- |
| 0x2f(FBH) | Exec_size | Pred | Dst | Src0 |


## Semantics




                    for (i = 0; < exec_size; ++i) {
                      if (ChEn[i]) {
                        UD cnt = 0;
                        if ( src0 is unsigned ) {
                          UD udScalar = src0[i];
                          while ( (udScalar & (1 << 31)) == 0 && cnt != 32 ) {
                            cnt ++;
                            udScalar = udScalar << 1;
                          }
                          dst[i] = src0[i] == 0 ? 0xFFFFFFFF : cnt;
                        }
                        else { // src0 is signed.
                          D dScalar = src0[i];
                          bit cval = dScalar[31];
                          while ((dScalar & (1 << 31)) == cval && cnt != 32 ) {
                            cnt ++;
                            dScalar = dScalar << 1;
                          }
                          dst[i] = (src0[i] == 0xFFFFFFFF) || (src0[i] == 0) ? 0xFFFFFFFF : cnt;
                        }
                      }
                    }

## Description



    Performs component-wise tracking of the first bit set from the MSB side in <src0> and stores the result into <dst>.

    The instruction behaves differently depending on the type and value of each component in src0:

    - If src0[i] is unsigned, the instruction counts the number of leading zeros.  If src0[i] has no bit set, the value 0xFFFFFFFF is returned.
    - If src0[i] is signed and >=0, the instruction counts the number of leading zeros.  If src0[i] is zero, the value 0xFFFFFFFF is returned.
    - If src0[i] is signed and negative, the instruction counts the number of leading ones.
    - If src0[i] is -1, the value 0xFFFFFFFF is returned.

- **Exec_size(ub):** Execution size
 
  - Bit[2..0]: size of the region for source and destination operands
 
    - 0b000:  1 element (scalar) 
    - 0b001:  2 elements 
    - 0b010:  4 elements 
    - 0b011:  8 elements 
    - 0b100:  16 elements 
    - 0b101:  32 elements 
  - Bit[7..4]: execution mask (explicit control over the enabled channels)
 
    - 0b0000:  M1 
    - 0b0001:  M2 
    - 0b0010:  M3 
    - 0b0011:  M4 
    - 0b0100:  M5 
    - 0b0101:  M6 
    - 0b0110:  M7 
    - 0b0111:  M8 
    - 0b1000:  M1_NM 
    - 0b1001:  M2_NM 
    - 0b1010:  M3_NM 
    - 0b1011:  M4_NM 
    - 0b1100:  M5_NM 
    - 0b1101:  M6_NM 
    - 0b1110:  M7_NM 
    - 0b1111:  M8_NM
- **Pred(uw):** Predication control

- **Dst(vec_operand):** The destination operand. Must have type UD. Operand class: general,indirect

- **Src0(vec_operand):** The first source operand. Must have type D,UD. Operand class: general,indirect,immediate

#### Properties
- **Source Modifier:** false 


## Text
```
    

		[(<P>)] FBH (<exec_size>) <dst> <src0>
```



## Notes


