__builtin_cntlzdm

Purpose

Returns the number of leading consecutive 0-bits in the result returned when the first argument corresponds to 1-bits in the second argument.

Note: This built-in function is valid only when the -mcpu option is set to target Power10 processors.

Syntax

d=__builtin_cntlzdm(a,b)

Result and argument types

The following table describes the types of the returned value and the function arguments.

Table 1. Types of the returned value and function arguments
d	a	b
unsigned long long	unsigned long long	unsigned long long

Result value

The result d is set to the number of consecutive 0-bits, starting on the left, in a that corresponds to 1-bits in b.

Here is an example for doubleword inputs:

Argument	Value
`a`	0x 0123 4567 89ab cdef
`b`	0x aaaa aaaa aaaa aaaa
`d`	5

In the above table, the first sixteen bits of a are 0000 0001 0010 0011. The first sixteen bits of b are 1010 1010 1010 1010. Applying the mask of b to a means that we only consider the even-numbered bits of a, which are 0 0 0 0 0 1 0 1. The number of leading zeros in this result is 5.