exp_synapse_utils.h

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/*
 * Copyright (c) 2017 The University of Manchester
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
 
#include <stdfix-exp.h>
#include <neuron/decay.h>
 
typedef struct exp_params_t {
    REAL tau;
    REAL init_input;
} exp_params_t;
 
typedef struct exp_state_t {
    decay_t decay;                  
    decay_t init;                   
    input_t synaptic_input_value;   
} exp_state_t;
 
static inline void decay_and_init(exp_state_t *state, exp_params_t *params,
        REAL time_step_ms, uint32_t n_steps_per_timestep) {
    REAL ts = kdivui(time_step_ms, n_steps_per_timestep);
    REAL ts_over_tau = kdivk(ts, params->tau);
    decay_t decay = expulr(-ts_over_tau);
    decay_t inv_decay = 1.0ulr - decay;
    REAL tau_over_ts = kdivk(params->tau, ts);
    decay_t init = decay_s1615_to_u032(tau_over_ts, inv_decay);
    state->decay = decay;
    state->init = init;
    state->synaptic_input_value = params->init_input;
}
 
static inline void exp_shaping(exp_state_t *exp_param) {
    // decay value according to decay constant
    exp_param->synaptic_input_value =
            decay_s1615(exp_param->synaptic_input_value, exp_param->decay);
}
 
static inline void add_input_exp(exp_state_t *parameter, input_t input) {
    parameter->synaptic_input_value = parameter->synaptic_input_value +
            decay_s1615(input, parameter->init);
}