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 # compute arctangent table for CORDIC computations in fttrigon.c import sys, math units = 64*65536.0 # 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 ""