| # 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 "" |
| |
