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authormarha <marha@users.sourceforge.net>2009-06-28 22:07:26 +0000
committermarha <marha@users.sourceforge.net>2009-06-28 22:07:26 +0000
commit3562e78743202e43aec8727005182a2558117eca (patch)
tree8f9113a77d12470c5c851a2a8e4cb02e89df7d43 /freetype/src/tools/cordic.py
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Diffstat (limited to 'freetype/src/tools/cordic.py')
-rw-r--r--freetype/src/tools/cordic.py79
1 files changed, 79 insertions, 0 deletions
diff --git a/freetype/src/tools/cordic.py b/freetype/src/tools/cordic.py
new file mode 100644
index 000000000..3f80c5f09
--- /dev/null
+++ b/freetype/src/tools/cordic.py
@@ -0,0 +1,79 @@
+# 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 ""
+