66 lines
1.4 KiB
Python
66 lines
1.4 KiB
Python
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"""fontTools.misc.fixedTools.py -- tools for working with fixed numbers.
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"""
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from __future__ import print_function, division
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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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>>> fixedToFloat(13107, 14)
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0.8
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>>> fixedToFloat(0, 14)
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0.0
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>>> fixedToFloat(0x4000, 14)
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1.0
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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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digits = (precisionBits + 2) // 3
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fmt = "%%.%df" % digits
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lo = fmt % (value - eps)
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hi = fmt % (value + eps)
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out = []
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length = min(len(lo), len(hi))
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for i in range(length):
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if lo[i] != hi[i]:
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break;
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out.append(lo[i])
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outlen = len(out)
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if outlen < length:
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out.append(max(lo[outlen], hi[outlen]))
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return float(strjoin(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(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 doctest
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doctest.testmod()
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