dnanmaxabs.c (1652B)
1 /** 2 * @license Apache-2.0 3 * 4 * Copyright (c) 2020 The Stdlib Authors. 5 * 6 * Licensed under the Apache License, Version 2.0 (the "License"); 7 * you may not use this file except in compliance with the License. 8 * You may obtain a copy of the License at 9 * 10 * http://www.apache.org/licenses/LICENSE-2.0 11 * 12 * Unless required by applicable law or agreed to in writing, software 13 * distributed under the License is distributed on an "AS IS" BASIS, 14 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 15 * See the License for the specific language governing permissions and 16 * limitations under the License. 17 */ 18 19 #include "stdlib/stats/base/dnanmaxabs.h" 20 #include "stdlib/math/base/assert/is_nan.h" 21 #include <stdint.h> 22 #include <math.h> 23 24 /** 25 * Computes the maximum absolute value of a double-precision floating-point strided array, ignoring `NaN` values. 26 * 27 * @param N number of indexed elements 28 * @param X input array 29 * @param stride stride length 30 * @return output value 31 */ 32 double stdlib_strided_dnanmaxabs( const int64_t N, const double *X, const int64_t stride ) { 33 double max; 34 int64_t ix; 35 int64_t i; 36 double v; 37 38 if ( N <= 0 ) { 39 return 0.0 / 0.0; // NaN 40 } 41 if ( N == 1 || stride == 0 ) { 42 return fabs( X[ 0 ] ); 43 } 44 if ( stride < 0 ) { 45 ix = (1-N) * stride; 46 } else { 47 ix = 0; 48 } 49 for ( i = 0; i < N; i++ ) { 50 v = X[ ix ]; 51 if ( v == v ) { 52 break; 53 } 54 ix += stride; 55 } 56 if ( i == N ) { 57 return 0.0 / 0.0; // NaN 58 } 59 max = fabs( v ); 60 i += 1; 61 for (; i < N; i++ ) { 62 ix += stride; 63 v = fabs( X[ ix ] ); 64 if ( stdlib_base_is_nan( v ) ) { 65 continue; 66 } 67 if ( v > max ) { 68 max = v; 69 } 70 } 71 return max; 72 }