param_generator_exponential_clipped.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.h>
#include <spin1_api.h>
#include <stdfix-full-iso.h>
#include <random.h>
#include <synapse_expander/rng.h>
#include <synapse_expander/generator_types.h>
 
#define MAX_REDRAWS 1000
 
typedef struct param_generator_exponential_clipped_params {
    accum beta;
    accum low;
    accum high;
} param_generator_exponential_clipped_params;
 
struct param_generator_exponential_clipped {
    param_generator_exponential_clipped_params params;
};
 
static void *param_generator_exponential_clipped_initialize(void **region) {
    // Allocate memory for the data
    struct param_generator_exponential_clipped *params =
            spin1_malloc(sizeof(struct param_generator_exponential_clipped));
 
    // Copy the parameters in
    param_generator_exponential_clipped_params *params_sdram = *region;
    params->params = *params_sdram;
    *region = &params_sdram[1];
    log_debug("exponential clipped beta = %k, low = %k, high = %k",
            params->params.beta, params->params.low, params->params.high);
 
    return params;
}
 
static void param_generator_exponential_clipped_free(void *generator) {
    sark_free(generator);
}
 
static accum param_generator_exponential_clipped_generate(void *generator) {
    // generate an exponentially distributed value
    struct param_generator_exponential_clipped *obj = generator;
    uint32_t n_draws = 0;
    accum value = 0k;
    do {
        value = rng_normal(core_rng);
        value = value * obj->params.beta;
        n_draws++;
    } while ((value < obj->params.low || value > obj->params.high)
            && (n_draws < MAX_REDRAWS));
    if (n_draws == MAX_REDRAWS) {
        log_error("Maximum number of redraws (%u) exceeded on clipped exponential "
                "distribution with beta=%k, low=%k, high=%k",
                n_draws, obj->params.beta, obj->params.low, obj->params.high);
        rt_error(RTE_SWERR);
    }
    return value;
}