[37] | 1 | /* mex ndsumC.c flops.obj |
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| 2 | */ |
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| 3 | /* Written by Tom Minka |
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| 4 | * (c) Microsoft Corporation. All rights reserved. |
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| 5 | */ |
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| 6 | #include "mex.h" |
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| 7 | #include "flops.h" |
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| 8 | |
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| 9 | void ndsum(double *dest, double *src, unsigned ndim, unsigned *size, |
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| 10 | unsigned total, unsigned *mask) |
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| 11 | { |
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| 12 | /* dest is the destination array. |
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| 13 | * src is the source array. |
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| 14 | * ndim is the number of dimensions in the source array (the length of size). |
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| 15 | * size[i] is the size of dimension i in the source array. |
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| 16 | * mask[i] indicates that dimension i is to be summed out. |
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| 17 | */ |
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| 18 | unsigned *masked_size,*cum_masked_size,*advance,*rewind; |
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| 19 | int *subs = mxCalloc(ndim,sizeof(int)); |
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| 20 | int i,j; |
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| 21 | masked_size = mxCalloc(ndim,sizeof(int)); |
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| 22 | for(i=0;i<ndim;i++) { |
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| 23 | masked_size[i] = mask[i] ? 1 : size[i]; |
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| 24 | } |
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| 25 | /* subs (initialized to zero) is the current position in the source array. |
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| 26 | * cum_masked_size[i] is the cumulative product of masked sizes up to i. |
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| 27 | * rewind[i] is cum_masked_size[i]*(masked_size[i]-1) |
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| 28 | * |
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| 29 | * The position in the destination array is |
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| 30 | * sum_i subs[i]*cum_masked_size[i]*!mask[i]. |
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| 31 | * To compute this incrementally, we add cum_masked_size[i]*!mask[i] |
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| 32 | * whenever we increment subs[i], and we subtract rewind[i] |
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| 33 | * whenever we set subs[i] back to 0 (from size[i]-1). |
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| 34 | */ |
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| 35 | cum_masked_size = mxCalloc(ndim,sizeof(int)); |
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| 36 | advance = mxCalloc(ndim,sizeof(int)); |
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| 37 | rewind = mxCalloc(ndim,sizeof(int)); |
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| 38 | cum_masked_size[0] = 1; |
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| 39 | for(i=0;i<ndim-1;i++) { |
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| 40 | cum_masked_size[i+1] = cum_masked_size[i]*masked_size[i]; |
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| 41 | } |
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| 42 | for(i=0;i<ndim;i++) { |
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| 43 | advance[i] = cum_masked_size[i]*!mask[i]; |
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| 44 | rewind[i] = cum_masked_size[i]*(masked_size[i]-1); |
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| 45 | } |
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| 46 | |
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| 47 | for(j=0;j<total;j++) { |
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| 48 | *dest += *src++; |
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| 49 | /* increment subs and update dest */ |
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| 50 | for(i=0;i<ndim;i++) { |
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| 51 | if(subs[i] == size[i]-1) { |
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| 52 | subs[i] = 0; |
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| 53 | dest -= rewind[i]; |
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| 54 | } |
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| 55 | else { |
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| 56 | subs[i]++; |
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| 57 | dest += advance[i]; |
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| 58 | break; |
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| 59 | } |
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| 60 | } |
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| 61 | } |
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| 62 | mxFree(rewind); |
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| 63 | mxFree(advance); |
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| 64 | mxFree(cum_masked_size); |
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| 65 | mxFree(masked_size); |
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| 66 | mxFree(subs); |
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| 67 | } |
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| 68 | |
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| 69 | void mexFunction(int nlhs, mxArray *plhs[], |
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| 70 | int nrhs, const mxArray *prhs[]) |
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| 71 | { |
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| 72 | /* prhs[0] is the multidimensional array. |
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| 73 | * prhs[1] is a vector listing the dimensions to sum out. |
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| 74 | */ |
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| 75 | int i,j; |
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| 76 | int ndim = mxGetNumberOfDimensions(prhs[0]); |
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| 77 | const int *size = mxGetDimensions(prhs[0]); |
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| 78 | double *src = mxGetPr(prhs[0]), *dest; |
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| 79 | double *dim = mxGetPr(prhs[1]); |
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| 80 | int nremove = mxGetNumberOfElements(prhs[1]); |
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| 81 | int dest_ndim = ndim - nremove; |
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| 82 | unsigned *dest_size; |
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| 83 | unsigned *mask; |
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| 84 | int total = mxGetNumberOfElements(prhs[0]), dest_total; |
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| 85 | |
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| 86 | if(dest_ndim == 0) { |
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| 87 | /* sum out everything */ |
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| 88 | plhs[0] = mxCreateDoubleMatrix(1,1,mxREAL); |
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| 89 | dest = mxGetPr(plhs[0]); |
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| 90 | for(i=0;i<total;i++) { |
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| 91 | *dest += src[i]; |
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| 92 | } |
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| 93 | addflops(total-1); |
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| 94 | return; |
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| 95 | } |
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| 96 | |
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| 97 | /* convert dim to a mask. */ |
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| 98 | /* mask[i] = 1 if dimension i is to be removed. */ |
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| 99 | mask = mxCalloc(ndim,sizeof(int)); |
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| 100 | /* dimensions in dim are indexed starting from 1. */ |
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| 101 | for(i=0;i<nremove;i++) mask[(int)dim[i]-1] = 1; |
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| 102 | /* compute the new size vector. */ |
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| 103 | dest_size = mxCalloc(dest_ndim,sizeof(int)); |
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| 104 | j = 0; |
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| 105 | for(i=0;i<ndim;i++) { |
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| 106 | if(!mask[i]) dest_size[j++] = size[i]; |
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| 107 | } |
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| 108 | plhs[0] = mxCreateNumericArray(dest_ndim, dest_size, mxDOUBLE_CLASS, mxREAL); |
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| 109 | dest_total = mxGetNumberOfElements(plhs[0]); |
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| 110 | dest = mxGetPr(plhs[0]); |
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| 111 | addflops(total-dest_total); |
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| 112 | if(dest_total == total) { |
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| 113 | /* don't sum anything */ |
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| 114 | memcpy(dest,src,total*sizeof(double)); |
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| 115 | return; |
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| 116 | } |
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| 117 | ndsum(dest,src,ndim,size,total,mask); |
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| 118 | } |
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