[EMAIL PROTECTED] writes:
> The problem is negative values. If the unit returns the hex value
> 'e7', it means -25, but python says it's 231:
Python is right. There is no "negative bit" in Python numbers, now
that unification of 'long' and 'int' is complete; numbers can grow
indefinitely large.
If you want a special interpretation of the value, you'll have to
calculate it.
Example assuming you want a one's-complement interpretation::
def value_from_reading(num):
""" Gets the integer value from the reading string.
num is a positive hexadecimal number as a string.
Numbers greater than 0x7F are interpreted as negative,
with magnitude greater than 0x7F being the negative value.
Only the lowest 15 bits are used for the magnitude.
>>> value_from_reading('00')
0
>>> value_from_reading('05')
5
>>> value_from_reading('7f')
127
>>> value_from_reading('80')
-128
>>> value_from_reading('e7')
-25
>>> value_from_reading('ff')
-1
>>> value_from_reading('100')
-128
>>> value_from_reading('fff')
-1
"""
num_base = 16
negative_threshold = 0x7F
int_val = int(num, num_base)
if int_val > negative_threshold:
magnitude = (int_val & negative_threshold)
int_val = -(1 + negative_threshold - magnitude)
return int_val
Adjust for whatever algorithm you want to use. Consult a book of
algorithms if you want a better implementation than my off-the-cuff
brute-force approach.
--
\ "Remorse: Regret that one waited so long to do it." -- Henry |
`\ L. Mencken |
_o__) |
Ben Finney
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