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Diffstat (limited to 'src/tools/cordic.py')
-rw-r--r-- | src/tools/cordic.py | 78 |
1 files changed, 78 insertions, 0 deletions
diff --git a/src/tools/cordic.py b/src/tools/cordic.py new file mode 100644 index 000000000..515fbcc5d --- /dev/null +++ b/src/tools/cordic.py @@ -0,0 +1,78 @@ +# compute arctangent table for CORDIC computations in fttrigon.c +import sys, math + +units = 180*65536 # don't change !! +scale = units/math.pi +shrink = 1.0 +comma = "" + +def calc_val( x ): + global units, shrink + angle = math.atan(x) + shrink = shrink * math.cos(angle) + return angle/math.pi * units + +def print_val( n, x ): + global comma + + lo = int(x) + hi = lo + 1 + alo = math.atan(lo) + ahi = math.atan(hi) + ax = math.atan(2.0**n) + + errlo = abs( alo - ax ) + errhi = abs( ahi - ax ) + + if ( errlo < errhi ): + hi = lo + + sys.stdout.write( comma + repr( int(hi) ) ) + comma = ", " + + +print "" +print "table of arctan( 1/2^n ) for PI = " + repr(units/65536.0) + " units" + +# compute range of "i" +r = [-1] +r = r + range(32) + +for n in r: + + if n >= 0: + x = 1.0/(2.0**n) # tangent value + else: + x = 2.0**(-n) + + angle = math.atan(x) # arctangent + angle2 = angle*scale # arctangent in FT_Angle units + + # determine which integer value for angle gives the best tangent + lo = int(angle2) + hi = lo + 1 + tlo = math.tan(lo/scale) + thi = math.tan(hi/scale) + + errlo = abs( tlo - x ) + errhi = abs( thi - x ) + + angle2 = hi + if errlo < errhi: + angle2 = lo + + if angle2 <= 0: + break + + sys.stdout.write( comma + repr( int(angle2) ) ) + comma = ", " + + shrink = shrink * math.cos( angle2/scale) + + +print +print "shrink factor = " + repr( shrink ) +print "shrink factor 2 = " + repr( shrink * (2.0**32) ) +print "expansion factor = " + repr(1/shrink) +print "" +
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