John Machin wrote: > 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
Thanks John, I will give it a good look. Regards, Philippe -- http://mail.python.org/mailman/listinfo/python-list
