4.3.5. CLZ

Count Leading Zeros.

Syntax

CLZ{cond} Rd, Rm

where:

cond

is an optional condition code (see Conditional execution).

Rd

is the destination register. Rd must not be r15.

Rm

is the operand register. Rm must not be r15.

Usage

The CLZ instruction counts the number of leading zeros in the value in Rm and returns the result in Rd. The result value is 32 if no bits are set in the source register, and zero if bit 31 is set.

Condition flags

This instruction does not change the flags.

Architectures

This ARM instruction is available in ARMv5T and above.

This 32-bit Thumb instruction is available in ARMv6T2 and above.

There is no 16-bit Thumb version of this instruction.

Examples

    CLZ     r4,r9
    CLZNE   r2,r3

Use the CLZ Thumb-2 instruction followed by a left shift of Rm by the resulting Rd value to normalize the value of register Rm. Use MOVS, rather than MOV, to flag the case where Rm is zero:

    CLZ r5, r9
    MOVS r9, r9, LSL r5
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