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50 lines
1.7 KiB
C
50 lines
1.7 KiB
C
/*
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* Copyright 2024 Google LLC
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#include "util/assert.h"
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#include "util/math_fixed.h"
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Fixed_S64_32 math_fixed_recursive_filter(Fixed_S64_32 x,
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int num_input_coefficients, int num_output_coefficients,
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const Fixed_S64_32 *cb, const Fixed_S64_32 *ca,
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Fixed_S64_32 *state_x, Fixed_S64_32 *state_y) {
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UTIL_ASSERT(num_input_coefficients >= 1);
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// shift the input over by one
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for (int k = num_input_coefficients - 1; k > 0; k--) {
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state_x[k] = state_x[k - 1];
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}
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state_x[0] = x;
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// Factor in the x * b elements
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Fixed_S64_32 ytmp = Fixed_S64_32_mul(cb[0], state_x[0]);
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for (int i = 1; i < num_input_coefficients; i++) {
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ytmp = Fixed_S64_32_add(ytmp, Fixed_S64_32_mul(cb[i], state_x[i]));
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}
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// Factor in the y * a coefficients
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for (int i = 0; i < num_output_coefficients; i++) {
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ytmp = Fixed_S64_32_sub(ytmp, Fixed_S64_32_mul(ca[i], state_y[i]));
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}
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// shift the y output elements
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for (int k = num_output_coefficients - 1; k > 0; k--) {
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state_y[k] = state_y[k-1];
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}
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state_y[0] = ytmp;
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return ytmp;
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}
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