zenilib: zenilib/jni/external/freetype2/src/tools/cordic.py Source File

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cordic.py
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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
cordic.calc_val
def calc_val
Definition: cordic.py:10
int
int
Definition: SDL_systhread.c:37
cordic.print_val
def print_val
Definition: cordic.py:16