Python Integer Representations & Arithmetic Library
Project description
Python Integer Representations & Arithmetic Library
This tool may be useful to system software developers (for example, compiler or binutils developers). Here are functions for representing integers in a convenient form and functions for arithmetic over integers of arbitrary format.
Install
$ git clone https://github.com/smurphik/pir
$ cd pir/
$ sudo python3 setup.py install clean
Formats
The integer arguments of almost all functions can be of any of 4 formats:
- decimal — usual python integer (
0
,7
,-2
, ...); - hexadecimal — string with or without prefix
'0x'
('0xf'
,'a7'
, and even'-0xcf'
); - binary — string with prefix
'0b'
('0b010110'
,'0b0'
, ...); - float — usual python float (Why not?
0.0
,17.
,-3.
, ...).
You can globally specify the default output format for arithmetic functions by call psetmode
or locally for each interface (by their parameter fmt
).
Representations
c2repr
gives two's complement representation in any output format in accordance with the current signedness and int width (signed 64-bit by default).
>>> from pirep import *
>>> c2repr(5, 'b')
'0b101'
>>> c2repr(-10)
'0xfffffffffffffff6'
>>> c2repr('8000000000000000', 'd')
-9223372036854775808
>>> c2repr('4000000000000000', 'd')
4611686018427387904
Meaning of prepr
by example. The operation sethi %hi(0x103c00), %o3
(see Sparc Instruction Set) is encoded to 1700040f
. We can clearly expand the code instructions on its fields. For this we need to know the numbers of the last bits of all fields:
>>> prepr('1700040f', (31, 29, 24, 21))
['00', '01011', '100', '0000000000010000001111']
>>> prepr('1700040f', (31, 29, 24, 21), 'h')
['0x0', '0xb', '0x4', '0x40f']
Why '0x40f'
and not 0x103c00
? It's ok. sethi
sets just 22 high bits:
# Left shift
>>> pls('0x40f', 10)
'0x103c00'
We could just decompose any integer by bytes:
>>> prepr(3932166)
['00111100', '00000000', '00000110']
More verbose way to decode — use vrepr()
with object of class Enc
:
>>> e = Enc('sethi', (('opc', 31), ('rd', 29), ('opc', 24), ('imm22', 21)))
>>> vrepr('1700040f', e, borders=True)
opc rd opc imm22
00 01011 100 0000000000010000001111
31-30 29-25 24-22 21-------------------0
>>> e.field(('opc', 31)).add_only_true(0)
>>> e.field(('rd', 29)).add_verbose(11, 'eleven')
>>> vrepr('1700040f', e, 'h')
opc rd opc imm22
0x0 0xb 0x4 0x40f
rd[29:25]: eleven
It is convenient to have a separate module that contains all the encodings you often use.
Arithmetic
You can globally specify the signedness and the integer width by psetmode
:
>>> from pirep import *
# Default mode: signed, 64-bit, hexadecimal default output
>>> pgetmode()
[True, 64, 'h']
>>> psub('0x100', 15)
'0xf1'
# Signed 8-bit int with decimal output by default
>>> psetmode(True, 8, 'd')
>>> psub('0x100', 15.)
-15
>>> psub('0x100', '0b1111', 'b')
'0b11110001'
pirep contains several other elementary arithmetic functions:
>>> psetmode(True, 8, 'd')
>>> pmul(3, padd(pdiv('f', '0b100'), prem(11, '0x3')))
15
>>> psetbits(15, (3, 5), '0b110')
55
>>> padd(pintmin(), pintmax())
-1
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