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# compute arctangent table for CORDIC computations in fttrigon.c
import sys, math
#units = 64*65536.0 # don't change !!
units = 256
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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