91 lines
2.1 KiB
Python
91 lines
2.1 KiB
Python
"""fontTools.misc.fixedTools.py -- tools for working with fixed numbers.
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"""
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from __future__ import print_function, division, absolute_import
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from fontTools.misc.py23 import *
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__all__ = [
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"fixedToFloat",
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"floatToFixed",
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]
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def fixedToFloat(value, precisionBits):
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"""Converts a fixed-point number to a float, choosing the float
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that has the shortest decimal reprentation. Eg. to convert a
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fixed number in a 2.14 format, use precisionBits=14. This is
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pretty slow compared to a simple division. Use sporadically.
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>>> "%g" % fixedToFloat(13107, 14)
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'0.8'
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>>> "%g" % fixedToFloat(0, 14)
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'0'
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>>> "%g" % fixedToFloat(0x4000, 14)
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'1'
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>>> "%g" % fixedToFloat(-16384, 14)
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'-1'
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>>> "%g" % fixedToFloat(-16383, 14)
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'-0.99994'
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>>> "%g" % fixedToFloat(16384, 14)
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'1'
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>>> "%g" % fixedToFloat(16383, 14)
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'0.99994'
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>>> "%g" % fixedToFloat(-639, 6)
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'-9.99'
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>>> "%g" % fixedToFloat(-640, 6)
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'-10'
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>>> "%g" % fixedToFloat(639, 6)
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'9.99'
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>>> "%g" % fixedToFloat(640, 6)
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'10'
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"""
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if not value: return 0.0
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scale = 1 << precisionBits
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value /= scale
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eps = .5 / scale
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lo = value - eps
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hi = value + eps
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# If the range of valid choices spans an integer, return the integer.
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if int(lo) != int(hi):
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return round(value)
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fmt = "%%.%df" % ((precisionBits + 2) // 3)
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lo = fmt % lo
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hi = fmt % hi
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i = 0
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length = min(len(lo), len(hi))
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while i < length and lo[i] == hi[i]:
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i += 1
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out = lo[:i]
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assert -1 != out.find('.') # Both ends should be the same past decimal point
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if i < length:
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# Append mid-point digit of half-open range (l,h].
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out = out + str((int(lo[i]) + int(hi[i]) + 1) // 2)
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return float(out)
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def floatToFixed(value, precisionBits):
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"""Converts a float to a fixed-point number given the number of
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precisionBits. Ie. int(round(value * (1<<precisionBits))).
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>>> floatToFixed(0.8, 14)
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13107
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>>> floatToFixed(1.0, 14)
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16384
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>>> floatToFixed(1, 14)
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16384
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>>> floatToFixed(-1.0, 14)
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-16384
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>>> floatToFixed(-1, 14)
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-16384
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>>> floatToFixed(0, 14)
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0
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"""
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return int(round(value * (1<<precisionBits)))
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if __name__ == "__main__":
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import sys
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import doctest
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sys.exit(doctest.testmod().failed)
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