cmMath.h/c : Added cmLFSR() and cmGenGoldCode().
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kevin
parent
c262a44e72
commit
032d359a90
131
cmMath.c
131
cmMath.c
@ -1,5 +1,10 @@
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#include "cmPrefix.h"
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#include "cmGlobal.h"
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#include "cmRpt.h"
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#include "cmErr.h"
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#include "cmCtx.h"
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#include "cmMem.h"
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#include "cmMallocDebug.h"
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#include "cmFloatTypes.h"
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#include "cmMath.h"
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#include <sys/types.h> // u_char
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@ -464,6 +469,128 @@ bool cmIsCloseU( unsigned x0, unsigned x1, double eps )
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{
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if( x0 == x1 )
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return true;
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return abs(x0-x1)/(x0+x1) < eps;
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if( x0 > x1 )
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return (x0-x1)/(x0+x1) < eps;
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else
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return (x1-x0)/(x0+x1) < eps;
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}
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//=================================================================
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// cmLFSR() implementation based on note at bottom of:
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// http://www.ece.cmu.edu/~koopman/lfsr/index.html
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void cmLFSR( unsigned lfsrN, unsigned tapMask, unsigned seed, unsigned* yV, unsigned yN )
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{
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assert( 0 < lfsrN && lfsrN < 32 );
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unsigned i;
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for(i=0; i<yN; ++i)
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{
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if( (yV[i] = seed & 1)==1 )
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seed = (seed >> 1) ^ tapMask;
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else
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seed = (seed >> 1);
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}
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}
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bool cmMLS_IsBalanced( const unsigned* xV, int xN)
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{
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int a = 0;
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unsigned i;
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for(i=0; i<xN; ++i)
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if( xV[i] == 1 )
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++a;
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return abs(a - (xN-a)) == 1;
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}
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unsigned _cmGenGoldCopy( int* y, unsigned yi, unsigned yN, unsigned* x, unsigned xN)
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{
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unsigned i;
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for(i=0; i<xN; ++i,++yi)
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y[yi] = x[i]==1 ? -1 : 1;
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assert(yi <= yN);
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return yi;
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}
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bool cmGenGoldCodes( unsigned lfsrN, unsigned poly_coeff0, unsigned poly_coeff1, unsigned goldN, int* yM, unsigned mlsN )
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{
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bool retFl = true;
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unsigned yi = 0;
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unsigned yN = goldN * mlsN;
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unsigned* mls0V = cmMemAllocZ(unsigned,mlsN);
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unsigned* mls1V = cmMemAllocZ(unsigned,mlsN);
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unsigned* xorV = cmMemAllocZ(unsigned,mlsN);
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unsigned i,j;
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cmLFSR(lfsrN, poly_coeff0, 1 << (lfsrN-1), mls0V, mlsN);
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cmLFSR(lfsrN, poly_coeff1, 1 << (lfsrN-1), mls1V, mlsN);
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if( cmMLS_IsBalanced(mls0V,mlsN) )
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yi = _cmGenGoldCopy(yM, yi, yN, mls0V, mlsN);
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if( yi<yN && cmMLS_IsBalanced(mls1V,mlsN) )
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yi = _cmGenGoldCopy(yM, yi, yN, mls1V, mlsN);
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for(i=0; yi < yN && i<mlsN-1; ++i )
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{
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for(j=0; j<mlsN; ++j)
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xorV[j] = (mls0V[j] + mls1V[ (i+j) % mlsN ]) % 2;
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if( cmMLS_IsBalanced(xorV,mlsN) )
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yi = _cmGenGoldCopy(yM,yi,yN,xorV,mlsN);
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}
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if(yi < yN )
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{
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//rc = cmErrMsg(err,kOpFailAtRC,"Gold code generation failed. Insuffient balanced pairs.");
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retFl = false;
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}
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cmMemFree(mls0V);
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cmMemFree(mls1V);
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cmMemFree(xorV);
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return retFl;
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}
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bool cmLFSR_Test()
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{
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// lfsrN = 5; % 5 6 7;
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// poly_coeff0 = 0x12; % 0x12 0x21 0x41;
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// poly_coeff1 = 0x1e; % 0x1e 0x36 0x72;
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unsigned lfsrN = 7;
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unsigned pc0 = 0x41;
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unsigned pc1 = 0x72;
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unsigned mlsN = (1 << lfsrN)-1;
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unsigned yN = mlsN*2;
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unsigned yV[ yN ];
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unsigned i;
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cmLFSR( lfsrN, pc0, 1 << (lfsrN-1), yV, yN );
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for(i=0; i<mlsN; ++i)
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if( yV[i] != yV[i+mlsN] )
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return false;
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//atVOU_PrintL(NULL,"0x12",yV,mlsN,2);
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cmLFSR( lfsrN, pc1, 1 << (lfsrN-1), yV, yN );
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//atVOU_PrintL(NULL,"0x17",yV,mlsN,2);
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for(i=0; i<mlsN; ++i)
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if( yV[i] != yV[i+mlsN] )
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return false;
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return true;
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}
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37
cmMath.h
37
cmMath.h
@ -74,4 +74,41 @@ bool cmIsCloseF( float x0, float x1, double eps );
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bool cmIsCloseI( int x0, int x1, double eps );
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bool cmIsCloseU( unsigned x0, unsigned x1, double eps );
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//=================================================================
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// Run a length 'lfsrN' linear feedback shift register (LFSR) for 'yN' iterations to
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// produce a length 'yN' bit string in yV[yN].
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// 'lfsrN' count of bits in the shift register range: 2<= lfsrN <= 32.
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// 'tapMask' is a bit mask which gives the tap indexes positions for the LFSR.
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// The least significant bit corresponds to the maximum delay tap position.
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// The min tap position is therefore denoted by the tap mask bit location 1 << (lfsrN-1).
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// A minimum of two taps must exist.
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// 'seed' sets the initial delay state.
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// 'yV[yN]' is the the output vector
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// 'yN' is count of elements in yV.
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// The function resturn kOkAtRC on success or kInvalidArgsRCRC if any arguments are invalid.
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// /sa cmLFSR_Test.
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void cmLFSR( unsigned lfsrN, unsigned tapMask, unsigned seed, unsigned* yV, unsigned yN );
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// Example and test code for cmLFSR()
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bool cmLFSR_Test();
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// Generate a set of 'goldN' Gold codes using the Maximum Length Sequences (MLS) generated
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// by a length 'lfsrN' linear feedback shift register.
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// 'err' is an error object to be set if the the function fails.
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// 'lfsrN' is the length of the Linear Feedback Shift Registers (LFSR) used to generate the MLS.
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// 'poly_coeff0' tap mask for the first LFSR.
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// 'coeff1' tap mask the the second LFSR.
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// 'goldN' is the count of Gold codes to generate.
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// 'yM[mlsN', goldN] is a column major output matrix where each column contains a Gold code.
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// 'mlsN' is the length of the maximum length sequence for each Gold code which can be
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// calculated as mlsN = (1 << a->lfsrN) - 1.
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// Note that values of 'lfsrN' and the 'poly_coeffx' must be carefully selected such that
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// they will produce a MLS. For example to generate a MLS with length 31 set 'lfsrN' to 5 and
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// then select poly_coeff from two different elements of the set {0x12 0x14 0x17 0x1B 0x1D 0x1E}.
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// See http://www.ece.cmu.edu/~koopman/lfsr/index.html for a complete set of MSL polynomial
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// coefficients for given LFSR lengths.
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// Returns false if insufficient balanced pairs exist.
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bool cmGenGoldCodes( unsigned lfsrN, unsigned poly_coeff0, unsigned poly_coeff1, unsigned goldN, int* yM, unsigned mlsN );
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#endif
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