//
// This confidential and proprietary software may be used only as
// authorised by a licensing agreement from ARM Limited
// (C) COPYRIGHT 2020-2021 ARM Limited
// ALL RIGHTS RESERVED
// The entire notice above must be reproduced on all authorised
// copies and copies may only be made to the extent permitted
// by a licensing agreement from ARM Limited.

=== Control Flow Operators

TOSA implements two control flow operators, for conditional branching and loop based control. Both have attributes that are TOSA sub-graphs.

==== COND_IF

Evaluates a Boolean condition and then takes one of two distinct execution paths. This implements the semantic if-then-else structure.

include::{generated}/operators/COND_IF.adoc[]

[source,c++]
----
ERROR_IF(tensor_list_shape(input_list) != tosa_input_shape(then_graph));
ERROR_IF(tensor_list_shape(input_list) != tosa_input_shape(else_graph));
ERROR_IF(tensor_list_shape(output_list) != tosa_output_shape(then_graph));
ERROR_IF(tensor_list_shape(output_list) != tosa_output_shape(else_graph));
ERROR_IF(tensor_size(shape) != 1);

if (condition[0]) {
    tosa_execute_graph(then_graph, input_list, output_list);
} else {
    tosa_execute_graph(else_graph, input_list, output_list);
}
----

==== WHILE_LOOP

Generates and evaluates a Bool condition and either executes a loop body or exits the loop. This action is performed repeatedly after updating and re-evaluating the Boolean condition every iteration. This implements the semantic foreach or while iterative loop structure.

include::{generated}/operators/WHILE_LOOP.adoc[]

[source,c++]
----
ERROR_IF(tensor_list_shape(input_list) != tosa_list_shape(output_list));
ERROR_IF(tensor_list_shape(input_list) != tosa_input_shape(cond_graph));
ERROR_IF(tensor_list_shape(input_list) != tosa_input_shape(body_graph));
ERROR_IF(tensor_list_shape(input_list) != tosa_output_shape(body_graph));
// Condition graph output must be a single element tensor with a single bool value
ERROR_IF(tensor_size(tosa_output_shape(cond_graph)) != 1);
ERROR_IF(tosa_output_type(cond_graph) != bool_t);

// The iteration number 'i' is included to give unique names to variables
// in each iteration of the loop and is not required by implementations
int32_t i=0;             // iteration number
tensor_list_t list[];    // array of tensor lists indexed by iteration
bool_t *condition[];     // array of condition tensors indexed by iteration
list[i] = input_list;    // copy input data as list[0]
tosa_execute_graph(cond_graph, list[i], [ condition[i] ]);   // initial condition
while (condition[i][0]) {
    tosa_execute_graph(body_graph, list[i], list[i+1]);
    i = i+1;
    tosa_execute_graph(cond_graph, list[i], [ condition[i] ]);
}
output_list = list[i];
----
