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Changed the arrays to be an array of x and an array of y.
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In the future I hope to be able to give an offset and have the array
of y generated by the library.
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@slowjud
slowjud committed Apr 23, 2010
1 parent 77ed413 commit b28fbaf
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Showing 2 changed files with 53 additions and 46 deletions.
2 changes: 1 addition & 1 deletion README.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -19,7 +19,7 @@ FFT is a Fast Fourier Transform C extension for Ruby
* Use an array or complex numbers in the form of [x, iy]

* To perform a farward transform
my_array = [[1,3],[2,5.2],[3.5,7],[4,22]]
my_array = [[1,2,3.5,4],[3,5.2,7,22]]
my_fft = my_array.fft

* To perform the reverse transform
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97 changes: 52 additions & 45 deletions ext/fft_api.c
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Original file line number Diff line number Diff line change
Expand Up @@ -10,50 +10,51 @@

// Validate the incoming array
static int validate( VALUE self ) {
long len, i;
VALUE *values;
long length;
VALUE *values = RARRAY_PTR( self );

// Check we're an Array
Check_Type( self, T_ARRAY );

// make sure we have an array of two arrays
if( RARRAY_LEN( self ) != 2 ) return FALSE;

// make sure the arrays are of the same length
if( RARRAY_LEN( values[0] ) != RARRAY_LEN( values[1] ) ) return FALSE;

// make sure the size of the array is a power of 2
len = RARRAY_LEN( self );
if( ( len < 2 ) || ( len & ( len - 1 ) ) ) return FALSE;

// check that we have an appropriate array
values = RARRAY_PTR( self );
for( i = 0; i < RARRAY_LEN( self ); i++ ) {
Check_Type( values[i], T_ARRAY );
if( RARRAY_LEN( values[i] ) != 2 ) return FALSE;
}
length = RARRAY_LEN( values[0] );
if( ( length < 2 ) || ( length & ( length - 1 ) ) ) return FALSE;

return TRUE;
}

static VALUE perform_fft( double **values, long len, int direction ){
VALUE outArray = rb_ary_new2( len );
static VALUE perform_fft( double **values, long length, int direction ){
VALUE outArray = rb_ary_new2( 2 );
VALUE xArray = rb_ary_new2( length );
VALUE yArray = rb_ary_new2( length );

long exponent, i, i1, j, k, i2, l, l1, l2;
double c1,c2,tx,ty,t1,t2,u1,u2,z;

// Caculate the exponent
exponent = 0;
i = len;
i = length;
while( i >>= 1 ){
exponent++;
}

// Do the bit reversal
i2 = len >> 1;
i2 = length >> 1;
j = 0;
for( i = 0; i < ( len - 1 ); i++ ){
for( i = 0; i < ( length - 1 ); i++ ){
if( i < j ){
tx = values[i][0];
ty = values[i][1];
values[i][0] = values[j][0];
values[i][1] = values[j][1];
values[j][0] = tx;
values[j][1] = ty;
tx = values[0][i];
ty = values[1][i];
values[0][i] = values[0][j];
values[1][i] = values[1][j];
values[0][j] = tx;
values[1][j] = ty;
}
k = i2;
while( k <= j ){
Expand All @@ -73,14 +74,14 @@ static VALUE perform_fft( double **values, long len, int direction ){
u1 = 1.0;
u2 = 0.0;
for( j = 0; j < l1; j++ ){
for( i = j; i < len; i += l2){
for( i = j; i < length; i += l2){
i1 = i + l1;
t1 = u1 * values[i1][0] - u2 * values[i1][1];
t2 = u1 * values[i1][1] + u2 * values[i1][0];
values[i1][0] = values[i][0] - t1;
values[i1][1] = values[i][1] - t2;
values[i][0] += t1;
values[i][1] += t2;
t1 = u1 * values[0][i1] - u2 * values[1][i1];
t2 = u1 * values[1][i1] + u2 * values[0][i1];
values[0][i1] = values[0][i] - t1;
values[1][i1] = values[1][i] - t2;
values[0][i] += t1;
values[1][i] += t2;
}
z = u1 * c1 - u2 * c2;
u2 = u1 * c2 + u2 * c1;
Expand All @@ -95,22 +96,26 @@ static VALUE perform_fft( double **values, long len, int direction ){

// Scaling for forward transform
if( direction == 1 ){
for( i = 0; i < len; i++ ){
values[i][0] /= len;
values[i][1] /= len;
for( i = 0; i < length; i++ ){
values[0][i] /= length;
values[1][i] /= length;
}
}
// convert the doubles into ruby numbers and stick them into a ruby array
for( i = 0; i < len; i++ ){
rb_ary_push( outArray, rb_ary_new3( 2, DBL2NUM( values[i][0] ), DBL2NUM( values[i][1] ) ) );
for( i = 0; i < length; i++ ){
rb_ary_push( xArray, DBL2NUM( values[0][i] ) );
rb_ary_push( yArray, DBL2NUM( values[1][i] ) );
}

rb_ary_push( outArray, xArray );
rb_ary_push( outArray, yArray );

return outArray;
}

// perform the fft
static VALUE prepare_fft( VALUE inArray, int direction ){
long i;
long i, length;
VALUE *values;
double **transformed;
VALUE outArray;
Expand All @@ -119,22 +124,24 @@ static VALUE prepare_fft( VALUE inArray, int direction ){
return Qnil;
}

// convert the ruby array into a C array of integers using FIX2INT(Fixnum)
transformed = malloc( sizeof( double* ) * RARRAY_LEN( inArray ) );
// convert the ruby array into a C array of integers using NUM2DBL(Fixnum)
values = RARRAY_PTR( inArray );
for( i = 0; i < RARRAY_LEN( inArray ); i++ ) {
length = RARRAY_LEN( values[0] );
transformed = malloc( sizeof( double ) * 2 );
transformed[0] = malloc( sizeof( double* ) * RARRAY_LEN( values[0] ) );
transformed[1] = malloc( sizeof( double* ) * RARRAY_LEN( values[1] ) );
for( i = 0; i < length; i++ ) {
// process values
transformed[i] = malloc( sizeof( double ) * 2 );
transformed[i][0] = NUM2DBL( RARRAY_PTR( values[i] )[0] );
transformed[i][1] = NUM2DBL( RARRAY_PTR( values[i] )[1] );
transformed[0][i] = NUM2DBL( RARRAY_PTR( values[0] )[i] );
transformed[1][i] = NUM2DBL( RARRAY_PTR( values[1] )[i] );
}

// do the actual transform
outArray = perform_fft( transformed, RARRAY_LEN( inArray ), direction );
outArray = perform_fft( transformed, length, direction );

for( i = 0; i < RARRAY_LEN( inArray ); i++ ) {
free( transformed[i] );
}
// No memory leaks here!
free( transformed[0] );
free( transformed[1] );
free( transformed );

return outArray;
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