## Description

The OpenCL C programming language implements the following built-in functions that operate on a work-group level. These built-in functions must be encountered by all work-items in a work-group executing the kernel. We use the generic type name gentype to indicate the built-in data types half59, int, uint, long, ulong, float or double60 as the type for the arguments.

[59] Only if the cl_khr_fp16 extension is supported and has been enabled.

[60] Only if double precision is supported.

 Function Description int work_group_all(int predicate) Evaluates predicate for all work-items in the work-group and returns a non-zero value if predicate evaluates to non-zero for all work-items in the work-group. int work_group_any(int predicate) Evaluates predicate for all work-items in the work-group and returns a non-zero value if predicate evaluates to non-zero for any work-items in the work-group. gentype work_group_broadcast(gentype a, size_t local_id) gentype work_group_broadcast(gentype a, size_t local_id_x, size_t local_id_y) gentype work_group_broadcast(gentype a, size_t local_id_x, size_t local_id_y, size_t local_id_z) Broadcast the value of x for work-item identified by local_id to all work-items in the work-group. local_id must be the same value for all work-items in the work-group. gentype work_group_reduce_(gentype x) Return result of reduction operation specified by for all values of x specified by work-items in a work-group. gentype work_group_scan_exclusive_(gentype x) Do an exclusive scan operation specified by of all values specified by work-items in the work-group. The scan results are returned for each work-item. The scan order is defined by increasing 1D linear global ID within the work-group. gentype work_group_scan_inclusive_(gentype x) Do an inclusive scan operation specified by of all values specified by work-items in the work-group. The scan results are returned for each work-item. The scan order is defined by increasing 1D linear global ID within the work-group.

The <op> in work_group_reduce_<op>, work_group_scan_exclusive_<op> and work_group_scan_inclusive_<op> defines the operator and can be add, min or max.

The inclusive scan operation takes a binary operator op with an identity I and n (where n is the size of the work-group) elements [a0, a1, …​ an-1] and returns [a0, (a0 op a1), …​ (a0 op a1 op …​ op an-1)]. If op = add, the identity I is 0. If op = min, the identity I is INT_MAX, UINT_MAX, LONG_MAX, ULONG_MAX, for int, uint, long, ulong types and is +INF for floating-point types. Similarly if op = max, the identity I is INT_MIN, 0, LONG_MIN, 0 and -INF.

Consider the following example:

void foo(int *p)
{
...
p[get_local_id(0)]);
}

For the example above, let’s assume that the work-group size is 8 and p points to the following elements [3 1 7 0 4 1 6 3]. Work-item 0 calls work_group_scan_inclusive_add with 3 and returns 3. Work-item 1 calls work_group_scan_inclusive_add with 1 and returns 4. The full set of values returned by work_group_scan_inclusive_add for work-items 0 …​ 7 are [3 4 11 11 15 16 22 25].

The exclusive scan operation takes a binary associative operator op with an identity I and n (where n is the size of the work-group) elements [a0, a1, …​ an-1] and returns [I, a0, (a0 op a1), …​ (a0 op a1 op …​ op an-2)]. For the example above, the exclusive scan add operation on the ordered set [3 1 7 0 4 1 6 3] would return [0 3 4 11 11 15 16 22].

 The order of floating-point operations is not guaranteed for the work_group_reduce_, work_group_scan_inclusive_ and work_group_scan_exclusive_ built-in functions that operate on half, float and double data types. The order of these floating-point operations is also non-deterministic for a given work-group.