65 lines
1.5 KiB
Python
65 lines
1.5 KiB
Python
# Functions for converting to and from fixed point in Python.
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from math import log10, floor
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def string_to_fixed_point(s, fracnum):
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l = s.split('.')
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if len(l) == 1:
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return int(s) << fracnum
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elif len(l) != 2:
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return None
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dec = 10
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frac = 0
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frac_decimal = int(l[1])
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# get the smallest power of ten higher then frac_decimal
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frac_decimal_len = floor(log10(frac_decimal) + 1)
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pow10 = 10**frac_decimal_len
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frac = 0
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# Example:
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# 0.4567 = 0.abcdefgh...
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# where abcdefgh are binary digits.
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# multiply both sides by two:
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# 0.9134 = a.bcdefgh ...
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# therefore a = 0. Then remove the most significant digit.
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# Then multiply by 2 again. Then
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# 18268 = b.cdefgh ...
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# therefore b = 1. Then take 8268, and so on.
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for i in range(0,fracnum):
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frac_decimal = frac_decimal * 2
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div, mod = divmod(frac_decimal, pow10)
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frac = div | (frac << 1)
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frac_decimal = mod
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whole = int(l[0])
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if whole < 0:
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return -((-whole) << fracnum | frac)
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else:
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return whole << fracnum | frac
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def fixed_point_to_string(fxp, fracnum):
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whole = str(fxp >> fracnum)
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mask = (1 << fracnum) - 1
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fracbit = fxp & mask
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n = 1
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frac = ""
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if fracbit == 0:
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return whole
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# The same method can be applied backwards.
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# 0.1110101 = 0.abcdefgh ...
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# where abcdefgh... are decimal digits. Then multiply by 10 to
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# get
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# 1001.0010010 = a.bcdefgh ...
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# therefore a = 0b1001 = 9. Then use a bitmask to get
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# 0.0010010 = 0.bcdefgh ...
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# etc.
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for i in range(0, fracnum):
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fracbit = fracbit * 10
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frac = frac + str(fracbit >> fracnum)
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fracbit = fracbit & mask
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return whole + "." + frac
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