Philippe Martin wrote:
> John Machin wrote:
>
> >
> > Philippe Martin wrote:
> >> Philippe Martin wrote:
> >>
> >> > Hi,
> >> >
> >> > I'm looking for an algo that would convert a list such as:
> >> >
> >> > I'm using python to prototype the algo: this will move to C in an
> >> > embedded system where an int has 16 bits - I do not wish to use any
> >> > python library.
> >> >
> >> > l1 = [1,2,3,4,6,7,8] #represents the decimal number 12345678
> >> > l2 = func (l1)
> >> > # l2 = [0x1, 0x2, 0xD, 0x6, 0x8, 0x7] #represents 0x12D687
> >> >
> >> >
> >> > Regards,
> >> >
> >> > Philippe
> >>
> >> Thanks to all,
> >>
> >> I decided to attack the problem another way and change the code in device
> >> #2 so it can now take the output from device #1.
> >>
> >> As device #2 only needs to compare, add, and subtract the stuff .. it
> >> makes my life much simpler.
> >>
> >
> > I'm confused.
> > 1. Was the original device #1 or #2?
> > 2. How many bits does the non-original device's C compiler support?
> > 3. If the original device is device #1, please explain where *it*
> > obtained an 8-digit decimal number expressed as 1 digit per byte (or
> > int) ...
>
>
> Well I don't want to bore you guys more than needed ;-) but:
>
> Device #1 has an 8 bit processor - uses a C cross-compiler that does not
> know anything above a 16 bit integer. I use this device to get information
> from users "1234...".
>
> Device #2 has an 8 bit processor - uses a subset of Java ... that does not
> know anything above a 16 bit integer.
>
>
> The information gathered in device number #1 must then be sent to device #2
> (after being encrypted .... ) to be compared, subtracted or added.
>
> The code I already have in device #2 makes the assumption that the
> information received is an array of bytes of length N which represents an
> actual value. ex: 0x67DF5 ==> [0x6, 0x7, 0xD, 0xF, 0x5] ... so it can
> compare/add/subtract values ... and do its job.
>
> As a python fan, I figured (back to my initial not very clear request), that
> I could prototype the above without making any major assumption as to the
> capabilities of the interpreter.
>
>
> I still believe that to be true.
>
Try this:
C:\junk>type bcd.py
def reconstitute_int(alist):
reghi, reglo = 0, 0
for digit in alist:
assert 0 <= digit <= 9
reghi, reglo = mul32by10(reghi, reglo)
reghi, reglo = add32(reghi, reglo, 0, digit)
return reghi, reglo
def uadd16(a, b):
return (a + b) & 0xFFFF
def shr32by4(hi, lo):
newhi = (hi >> 4) & 0xFFFF
newlo = ((lo >> 4) | ((hi & 0xF) << 12)) & 0xFFFF
return newhi, newlo
def add32(hia, loa, hib, lob):
lox = uadd16(loa, lob)
hix = uadd16(hia, hib)
inx = ((lox & 0x8000) >> 13) + ((lob & 0x8000) >> 14) + ((loa &
0x8000) >> 1
5)
carry = [0, 1, 1, 1, 0, 0, 0, 1][inx]
# The above is admittedly ugly but sheesh I haven't even had my
# second cup of coffee yet today :-)
# Anybody who's good at solving equations in Boolean algebra,
# pls beautify this!!
if carry:
hix = uadd16(hix, 1)
expected = (hia+hib)*65536 + loa + lob
actual = hix*65536 + lox
if actual != expected:
print (hia, loa), (hib, lob), (hix, lox), actual, expected,
inx, carry
return hix, lox
def mul32by10(hi, lo):
tmphi, tmplo = add32(hi, lo, hi, lo) # 2 times
tmphi, tmplo = add32(tmphi, tmplo, tmphi, tmplo) # 4 times
tmphi, tmplo = add32(tmphi, tmplo, hi, lo) # 5 times
tmphi, tmplo = add32(tmphi, tmplo, tmphi, tmplo) # 10 times
return tmphi, tmplo
def make_hex32(aninthi, anintlo):
result = []
while aninthi or anintlo:
result.append(anintlo & 0xF)
aninthi, anintlo = shr32by4(aninthi, anintlo)
return result
def reverse_list(alist):
n = len(alist)
for i in xrange(n >> 1):
reg1 = alist[n - 1 - i]
reg2 = alist[i]
alist[i] = reg1
alist[n - 1 - i] = reg2
C:\junk>python
Python 2.4.3 (#69, Mar 29 2006, 17:35:34) [MSC v.1310 32 bit (Intel)]
on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import bcd
>>> num = bcd.reconstitute_int([1,2,3,4,5,6,7,8])
>>> num
(188, 24910)
>>> num[0]*65536 + num[1]
12345678
>>> result = bcd.make_hex32(*num)
>>> result
[14, 4, 1, 6, 12, 11]
>>> bcd.reverse_list(result)
>>> result
[11, 12, 6, 1, 4, 14]
>>> ['0x%x' % digit for digit in result]
['0xb', '0xc', '0x6', '0x1', '0x4', '0xe']
>>> ^Z
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