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micropython/tests/float/float_parse_doubleprec.py

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py/parsenum: Improve parsing of floating point numbers. This patch improves parsing of floating point numbers by converting all the digits (integer and fractional) together into a number 1 or greater, and then applying the correct power of 10 at the very end. In particular the multiple "multiply by 0.1" operations to build a fraction are now combined together and applied at the same time as the exponent, at the very end. This helps to retain precision during parsing of floats, and also includes a check that the number doesn't overflow during the parsing. One benefit is that a float will have the same value no matter where the decimal point is located, eg 1.23 == 123e-2.
7 years ago
# test parsing of floats, requiring double-precision
# very large integer part with a very negative exponent should cancel out
print(float('9' * 400 + 'e-100'))
print(float('9' * 400 + 'e-200'))
print(float('9' * 400 + 'e-400'))
# many fractional digits
print(float('.' + '9' * 400))
print(float('.' + '9' * 400 + 'e100'))
print(float('.' + '9' * 400 + 'e-100'))
# tiny fraction with large exponent
tests/float: Adjust float-parsing tests to pass with only a small error. Float parsing (both single and double precision) may have a relative error of order the floating point precision, so adjust tests to take this into account by not printing all of the digits of the answer.
7 years ago
print('%.14e' % float('.' + '0' * 400 + '9e100'))
print('%.14e' % float('.' + '0' * 400 + '9e200'))
print('%.14e' % float('.' + '0' * 400 + '9e400'))
py/parsenum: Fix parsing of floats that are close to subnormal. Prior to this patch, a float literal that was close to subnormal would have a loss of precision when parsed. The worst case was something like float('10000000000000000000e-326') which returned 0.0.
7 years ago
# ensure that accuracy is retained when value is close to a subnormal
print(float('1.00000000000000000000e-307'))
print(float('10.0000000000000000000e-308'))
print(float('100.000000000000000000e-309'))