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annotate dep/fmt/support/compute-powers.py @ 367:8d45d892be88 default tip

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*: instead of pugixml, use Qt XML features this means we have one extra Qt dependency though...
author Paper <paper@tflc.us>
date Sun, 17 Nov 2024 22:55:47 -0500
parents 1faa72660932
children
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343
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Paper <paper@paper.us.eu.org>
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1 #!/usr/bin/env python
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Paper <paper@paper.us.eu.org>
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2 # Compute 10 ** exp with exp in the range [min_exponent, max_exponent] and print
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3 # normalized (with most-significant bit equal to 1) significands in hexadecimal.
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4
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Paper <paper@paper.us.eu.org>
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5 from __future__ import print_function
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6
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Paper <paper@paper.us.eu.org>
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7 min_exponent = -348
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8 max_exponent = 340
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9 step = 8
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10 significand_size = 64
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Paper <paper@paper.us.eu.org>
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11 exp_offset = 2000
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12
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Paper <paper@paper.us.eu.org>
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13 class fp:
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Paper <paper@paper.us.eu.org>
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14 pass
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15
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Paper <paper@paper.us.eu.org>
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16 powers = []
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17 for i, exp in enumerate(range(min_exponent, max_exponent + 1, step)):
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Paper <paper@paper.us.eu.org>
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18 result = fp()
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19 n = 10 ** exp if exp >= 0 else 2 ** exp_offset / 10 ** -exp
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Paper <paper@paper.us.eu.org>
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20 k = significand_size + 1
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Paper <paper@paper.us.eu.org>
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21 # Convert to binary and round.
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22 binary = '{:b}'.format(n)
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23 result.f = (int('{:0<{}}'.format(binary[:k], k), 2) + 1) / 2
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24 result.e = len(binary) - (exp_offset if exp < 0 else 0) - significand_size
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25 powers.append(result)
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26 # Sanity check.
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27 exp_offset10 = 400
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28 actual = result.f * 10 ** exp_offset10
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29 if result.e > 0:
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30 actual *= 2 ** result.e
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31 else:
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32 for j in range(-result.e):
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33 actual /= 2
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34 expected = 10 ** (exp_offset10 + exp)
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35 precision = len('{}'.format(expected)) - len('{}'.format(actual - expected))
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36 if precision < 19:
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37 print('low precision:', precision)
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38 exit(1)
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39
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Paper <paper@paper.us.eu.org>
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40 print('Significands:', end='')
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41 for i, fp in enumerate(powers):
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42 if i % 3 == 0:
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43 print(end='\n ')
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44 print(' {:0<#16x}'.format(fp.f, ), end=',')
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45
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46 print('\n\nExponents:', end='')
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47 for i, fp in enumerate(powers):
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48 if i % 11 == 0:
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49 print(end='\n ')
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Paper <paper@paper.us.eu.org>
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50 print(' {:5}'.format(fp.e), end=',')
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51
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Paper <paper@paper.us.eu.org>
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52 print('\n\nMax exponent difference:',
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Paper <paper@paper.us.eu.org>
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53 max([x.e - powers[i - 1].e for i, x in enumerate(powers)][1:]))