reactos/dll/3rdparty/freetype/src/tools/cordic.py

   1 # compute arctangent table for CORDIC computations in fttrigon.c
   2 import sys, math
   3
   4 #units  = 64*65536.0   # don't change !!
   5 units  = 256
   6 scale  = units/math.pi
   7 shrink = 1.0
   8 comma  = ""
   9
  10 def calc_val( x ):
  11     global units, shrink
  12     angle  = math.atan(x)
  13     shrink = shrink * math.cos(angle)
  14     return angle/math.pi * units
  15
  16 def  print_val( n, x ):
  17     global comma
  18
  19     lo  = int(x)
  20     hi  = lo + 1
  21     alo = math.atan(lo)
  22     ahi = math.atan(hi)
  23     ax  = math.atan(2.0**n)
  24
  25     errlo = abs( alo - ax )
  26     errhi = abs( ahi - ax )
  27
  28     if ( errlo < errhi ):
  29       hi = lo
  30
  31     sys.stdout.write( comma + repr( int(hi) ) )
  32     comma = ", "
  33
  34
  35 print ""
  36 print "table of arctan( 1/2^n ) for PI = " + repr(units/65536.0) + " units"
  37
  38 # compute range of "i"
  39 r = [-1]
  40 r = r + range(32)
  41
  42 for n in r:
  43
  44     if n >= 0:
  45         x = 1.0/(2.0**n)    # tangent value
  46     else:
  47         x = 2.0**(-n)
  48
  49     angle  = math.atan(x)    # arctangent
  50     angle2 = angle*scale     # arctangent in FT_Angle units
  51
  52     # determine which integer value for angle gives the best tangent
  53     lo  = int(angle2)
  54     hi  = lo + 1
  55     tlo = math.tan(lo/scale)
  56     thi = math.tan(hi/scale)
  57
  58     errlo = abs( tlo - x )
  59     errhi = abs( thi - x )
  60
  61     angle2 = hi
  62     if errlo < errhi:
  63         angle2 = lo
  64
  65     if angle2 <= 0:
  66         break
  67
  68     sys.stdout.write( comma + repr( int(angle2) ) )
  69     comma = ", "
  70
  71     shrink = shrink * math.cos( angle2/scale)
  72
  73
  74 print
  75 print "shrink factor    = " + repr( shrink )
  76 print "shrink factor 2  = " + repr( shrink * (2.0**32) )
  77 print "expansion factor = " + repr(1/shrink)
  78 print ""
  79