clz.h File Reference

Leading and trailing zero counts: the argument type, the two calls, and the clz dispatch table. More...

#include "mmgr.h"

Go to the source code of this file.

Data Structures
struct	ClzCfg
	Argument for both clz calls: the value to count zeros in. More...
struct	ClzNs
	Type of the clz dispatch table. More...

Functions
embed_iword	mmgr_clz_lead (const ClzCfg *args)
	Counts the zero bits above the highest set bit of args->val.
embed_iword	mmgr_clz_trail (const ClzCfg *args)
	Counts the zero bits below the lowest set bit of args->val.

Variables
static const ClzNs	clz
	Dispatch table instance named clz, with each member set to its mmgr_clz_ function.

Detailed Description

Leading and trailing zero counts: the argument type, the two calls, and the clz dispatch table.

Author

dstroy0 (Douglas Quigg) dquig.nosp@m.g123.nosp@m.@gmai.nosp@m.l.co.nosp@m.m

Date

2026-08-29

Note

A zero count is how a scan turns a lane mask into a lane index, and so these sit under the SWAR walks instead of being a general utility.

Both run branchless and in a fixed number of steps. A caller pays the same whatever the value is. That is the ground on which they are written out and not reached through a builtin, which is absent on some targets and a call on others.

Warning

Neither distinguishes a value of 0 from a value with one bit set at the end it counts from. A caller that can be handed 0 tests for it first.

Definition in file clz.h.

Function Documentation

mmgr_clz_lead()

embed_iword mmgr_clz_lead

(

const ClzCfg *

args

)

Counts the zero bits above the highest set bit of args->val.

Parameters

[in]

args

Value to measure [BORROWS].

Returns

Leading zero count, 0 through 63.

Note

Runs in a fixed number of steps, none of which branches on the value.

Warning

An args->val of 0 returns 63, the same answer as an args->val of 1.

References mmgr_clz_lead().

Referenced by mmgr_clz_lead().

mmgr_clz_trail()

embed_iword mmgr_clz_trail

(

const ClzCfg *

args

)

Counts the zero bits below the lowest set bit of args->val.

Parameters

[in]

args

Value to measure [BORROWS].

Returns

Trailing zero count, 0 through 63.

Note

Runs in a fixed number of steps, none of which branches on the value.

Warning

An args->val of 0 returns 63, the same answer as an args->val of 2^63.

References mmgr_clz_trail().

Referenced by mmgr_clz_trail().

Variable Documentation

clz

const ClzNs clz

static

Dispatch table instance named clz, with each member set to its mmgr_clz_ function.

Definition at line 73 of file clz.h.