Re: How to get an integer from a sequence of bytes
Fábio Santos fabiosantos...@gmail.com wrote: On 5 Jun 2013 06:23, Tim Roberts t...@probo.com wrote: A single machine word was 60 bits, so a single register read got you 10 characters. 10 characters! Now that sounds like it's enough to actually store a word. However long words can inadverten be cropped. Well, Cybers weren't often used for heavy text processing. Most of the time, a word was limited to 7 characters, so you could fit an 18-bit address in the bottom of the register. -- Tim Roberts, t...@probo.com Providenza Boekelheide, Inc. -- http://mail.python.org/mailman/listinfo/python-list
Re: How to get an integer from a sequence of bytes
On Tue, Jun 4, 2013 at 3:49 PM, Chris Angelico ros...@gmail.com wrote: So... can we cite http://xkcd.com/859/ in two threads at once, or does that create twice as much tension? No, you just look at one of them upside-down, and then they cancel each other out. -- http://mail.python.org/mailman/listinfo/python-list
Re: How to get an integer from a sequence of bytes
On 5 Jun 2013 06:23, Tim Roberts t...@probo.com wrote: A single machine word was 60 bits, so a single register read got you 10 characters. 10 characters! Now that sounds like it's enough to actually store a word. However long words can inadverten be cropped. -- http://mail.python.org/mailman/listinfo/python-list
Re: How to get an integer from a sequence of bytes
On 2013-06-12, F?bio Santos fabiosantos...@gmail.com wrote: On 5 Jun 2013 06:23, Tim Roberts t...@probo.com wrote: A single machine word was 60 bits, so a single register read got you 10 characters. 10 characters! Now that sounds like it's enough to actually store a word. However long words can inadverten be cropped. Only the first 10 characters in variable names were significant when you wrote Pascal programs (I don't remember if that was true for FORTRAN, but I bet it was). -- Grant Edwards grant.b.edwardsYow! I'm gliding over a at NUCLEAR WASTE DUMP near gmail.comATLANTA, Georgia!! -- http://mail.python.org/mailman/listinfo/python-list
Re: How to get an integer from a sequence of bytes
On 2013-06-03, Dan Stromberg drsali...@gmail.com wrote: On Mon, Jun 3, 2013 at 7:31 AM, Grant Edwards invalid@invalid.invalidwrote: That's a common assumption, but historically, a byte was merely the smallest addressable unit of memory. The size of a byte on widely used used CPUs ranged from 4 bits to 60 bits. Quoting from http://en.wikipedia.org/wiki/Byte The size of the byte has historically been hardware dependent and no definitive standards existed that mandated the size. That's why IEEE standards always use the word octet when referring a value containing 8 bits. When I was a Freshman in college, I used a CDC Cyber a lot; it had 6 bit bytes and 60 bit words. This was in 1985. But you couldn't address individual 6-bit hextets in memory could you? My recollection is that incrementing a memory address got you the next 60-bit chunk -- that means that by the older terminology a byte was 60 bits. A character was 6 bits, and a single register or memory location could hold 6 characters. Today though, it would be difficult to sell a conventional (Von Neumann) computer that didn't have 8 bit bytes. There are tons (as in millions of units per month) of CPUs still being sold in the DSP market with 16, 20, 24, and 32 bit bytes. (When writing C on a TMS320Cxx CPU sizeof (char) == sizeof (int) == sizeof (long) == sizeof (float) == sizeof (double) == 1. They all contain 32 bits. Quantum computers would still sell if they were odd this way - they're going to be really different anyway. -- Grant Edwards grant.b.edwardsYow! Either CONFESS now or at we go to PEOPLE'S COURT!! gmail.com -- http://mail.python.org/mailman/listinfo/python-list
Re: How to get an integer from a sequence of bytes
On 2013-06-03, Carlos Nepomuceno carlosnepomuc...@outlook.com wrote: Date: Mon, 3 Jun 2013 15:41:41 -0700 Subject: Re: How to get an integer from a sequence of bytes From: drsali...@gmail.com To: python-list@python.org [...] Today though, it would be difficult to sell a conventional (Von Neumann) computer that didn't have 8 bit bytes. Quantum computers would still sell if they were odd this way - they're going to be really different anyway. Nowadays it would be a hard task to find a Von Neumann architecture machine. Most of current CPUs are variants of the Harvard architecture: they separate instructions from data at the cache level. VN designs are still very common in smaller CPUs (embedded stuff). Even modern desktop CPUs are logically still Von Neumann designs from the programmer's point of view (there's only a single address space for both data and instructions). The fact that there are two sparate caches is almost entirely hidden from the user. If you start to do stuff like write self-modifying code, then _may_ start having to worry about cache coherency. -- Grant Edwards grant.b.edwardsYow! I request a weekend in at Havana with Phil Silvers! gmail.com -- http://mail.python.org/mailman/listinfo/python-list
RE: How to get an integer from a sequence of bytes
From: invalid@invalid.invalid Subject: Re: How to get an integer from a sequence of bytes Date: Tue, 4 Jun 2013 13:42:46 + To: python-list@python.org [...] VN designs are still very common in smaller CPUs (embedded stuff). DSPs perhaps... not CPUs. Even ARMs are Harvard variants. Even modern desktop CPUs are logically still Von Neumann designs from the programmer's point of view (there's only a single address space for both data and instructions). The fact that there are two sparate caches is almost entirely hidden from the user. If you start to do stuff like write self-modifying code, then _may_ start having to worry about cache coherency. Code/data separation isn't the only aspect. VN architecture is totally serial, even for RAM. It's been a while since we've got into the multi-core, multipath world. Even in embedded devices. -- Grant Edwards grant.b.edwardsYow! I request a weekend in at Havana with Phil Silvers! gmail.com -- http://mail.python.org/mailman/listinfo/python-list -- http://mail.python.org/mailman/listinfo/python-list
Re: How to get an integer from a sequence of bytes
On 4 June 2013 14:39, Grant Edwards invalid@invalid.invalid wrote: On 2013-06-03, Dan Stromberg drsali...@gmail.com wrote: Today though, it would be difficult to sell a conventional (Von Neumann) computer that didn't have 8 bit bytes. There are tons (as in millions of units per month) of CPUs still being sold in the DSP market with 16, 20, 24, and 32 bit bytes. (When writing C on a TMS320Cxx CPU sizeof (char) == sizeof (int) == sizeof (long) == sizeof (float) == sizeof (double) == 1. They all contain 32 bits. ) *) for the bracket not in the reply Sorry. -- http://mail.python.org/mailman/listinfo/python-list
Re: How to get an integer from a sequence of bytes
On Wed, Jun 5, 2013 at 5:51 AM, Joshua Landau joshua.landau...@gmail.com wrote: On 4 June 2013 14:39, Grant Edwards invalid@invalid.invalid wrote: On 2013-06-03, Dan Stromberg drsali...@gmail.com wrote: Today though, it would be difficult to sell a conventional (Von Neumann) computer that didn't have 8 bit bytes. There are tons (as in millions of units per month) of CPUs still being sold in the DSP market with 16, 20, 24, and 32 bit bytes. (When writing C on a TMS320Cxx CPU sizeof (char) == sizeof (int) == sizeof (long) == sizeof (float) == sizeof (double) == 1. They all contain 32 bits. ) *) for the bracket not in the reply Sorry. So... can we cite http://xkcd.com/859/ in two threads at once, or does that create twice as much tension? Once an XKCD is un-cited, will it be garbage collected promptly, or do they contain refloops? ChrisA -- http://mail.python.org/mailman/listinfo/python-list
Re: How to get an integer from a sequence of bytes
Grant Edwards invalid@invalid.invalid wrote: On 2013-06-03, Dan Stromberg drsali...@gmail.com wrote: When I was a Freshman in college, I used a CDC Cyber a lot; it had 6 bit bytes and 60 bit words. This was in 1985. But you couldn't address individual 6-bit hextets in memory could you? My recollection is that incrementing a memory address got you the next 60-bit chunk -- that means that by the older terminology a byte was 60 bits. A character was 6 bits, and a single register or memory location could hold 6 characters. A single machine word was 60 bits, so a single register read got you 10 characters. There were three sets of registers -- the X registers were 60 bits, the A and B registers were 18 bits, which was the size of the largest possible address. CDC didn't actually use the term byte. That was IBM's domain. When ASCII became unavoidable, most programs changed to using 5x 12-bit bytes per word. Ah, memories. I spent 10 years working for Control Data. -- Tim Roberts, t...@probo.com Providenza Boekelheide, Inc. -- http://mail.python.org/mailman/listinfo/python-list
Re: How to get an integer from a sequence of bytes
On 2013-06-03, Dennis Lee Bieber wlfr...@ix.netcom.com wrote: On Sun, 02 Jun 2013 21:25:45 +0200, Mok-Kong Shen mok-kong.s...@t-online.de declaimed the following in gmane.comp.python.general: b'7' is the byte with the character 7 in a certain code, so that's ok. In other PLs one assigns an int to a byte, with that int in either In other languages byte is an 8-bit signed/unsigned numeric. That's a common assumption, but historically, a byte was merely the smallest addressable unit of memory. The size of a byte on widely used used CPUs ranged from 4 bits to 60 bits. Quoting from http://en.wikipedia.org/wiki/Byte The size of the byte has historically been hardware dependent and no definitive standards existed that mandated the size. That's why IEEE standards always use the word octet when referring a value containing 8 bits. Only recently has it become common to assume that an byte contains 8 bits. -- Grant Edwards grant.b.edwardsYow! It's a lot of fun at being alive ... I wonder if gmail.commy bed is made?!? -- http://mail.python.org/mailman/listinfo/python-list
Re: How to get an integer from a sequence of bytes
On 06/03/2013 10:31 AM, Grant Edwards wrote: On 2013-06-03, Dennis Lee Bieber wlfr...@ix.netcom.com wrote: On Sun, 02 Jun 2013 21:25:45 +0200, Mok-Kong Shen mok-kong.s...@t-online.de declaimed the following in gmane.comp.python.general: b'7' is the byte with the character 7 in a certain code, so that's ok. In other PLs one assigns an int to a byte, with that int in either In other languages byte is an 8-bit signed/unsigned numeric. That's a common assumption, but historically, a byte was merely the smallest addressable unit of memory. The size of a byte on widely used used CPUs ranged from 4 bits to 60 bits. Hehe I recall rewriting the unpacking algorithm to get the 10 characters from each byte, on such a machine. -- DaveA -- http://mail.python.org/mailman/listinfo/python-list
Re: How to get an integer from a sequence of bytes
On 2013-06-03, Dave Angel d...@davea.name wrote: On 06/03/2013 10:31 AM, Grant Edwards wrote: On 2013-06-03, Dennis Lee Bieber wlfr...@ix.netcom.com wrote: On Sun, 02 Jun 2013 21:25:45 +0200, Mok-Kong Shen mok-kong.s...@t-online.de declaimed the following in gmane.comp.python.general: b'7' is the byte with the character 7 in a certain code, so that's ok. In other PLs one assigns an int to a byte, with that int in either In other languages byte is an 8-bit signed/unsigned numeric. That's a common assumption, but historically, a byte was merely the smallest addressable unit of memory. The size of a byte on widely used used CPUs ranged from 4 bits to 60 bits. Hehe I recall rewriting the unpacking algorithm to get the 10 characters from each byte, on such a machine. Yep. IIRC there were CDC machines (Cyber 6600?) with a 60-bit wide byte and a 6-bit wide upper-case-only character set. ISTM that the Pascal compiler limited you to 6 significant characters in variable names so that it could use a simple single register compare while doing symbol lookups... I think some IBM machines had 60-bit bytes as well. -- Grant Edwards grant.b.edwardsYow! DIDI ... is that a at MARTIAN name, or, are we gmail.comin ISRAEL? -- http://mail.python.org/mailman/listinfo/python-list
Re: How to get an integer from a sequence of bytes
On Mon, Jun 3, 2013 at 7:31 AM, Grant Edwards invalid@invalid.invalidwrote: That's a common assumption, but historically, a byte was merely the smallest addressable unit of memory. The size of a byte on widely used used CPUs ranged from 4 bits to 60 bits. Quoting from http://en.wikipedia.org/wiki/Byte The size of the byte has historically been hardware dependent and no definitive standards existed that mandated the size. That's why IEEE standards always use the word octet when referring a value containing 8 bits. When I was a Freshman in college, I used a CDC Cyber a lot; it had 6 bit bytes and 60 bit words. This was in 1985. Today though, it would be difficult to sell a conventional (Von Neumann) computer that didn't have 8 bit bytes. Quantum computers would still sell if they were odd this way - they're going to be really different anyway. -- http://mail.python.org/mailman/listinfo/python-list
RE: How to get an integer from a sequence of bytes
Date: Mon, 3 Jun 2013 15:41:41 -0700 Subject: Re: How to get an integer from a sequence of bytes From: drsali...@gmail.com To: python-list@python.org [...] Today though, it would be difficult to sell a conventional (Von Neumann) computer that didn't have 8 bit bytes. Quantum computers would still sell if they were odd this way - they're going to be really different anyway. Nowadays it would be a hard task to find a Von Neumann architecture machine. Most of current CPUs are variants of the Harvard architecture: they separate instructions from data at the cache level. -- http://mail.python.org/mailman/listinfo/python-list
Re: How to get an integer from a sequence of bytes
On Mon, Jun 3, 2013 at 4:18 PM, Carlos Nepomuceno carlosnepomuc...@outlook.com wrote: Date: Mon, 3 Jun 2013 15:41:41 -0700 Subject: Re: How to get an integer from a sequence of bytes From: drsali...@gmail.com To: python-list@python.org [...] Today though, it would be difficult to sell a conventional (Von Neumann) computer that didn't have 8 bit bytes. Quantum computers would still sell if they were odd this way - they're going to be really different anyway. Nowadays it would be a hard task to find a Von Neumann architecture machine. Most of current CPUs are variants of the Harvard architecture: they separate instructions from data at the cache level. I stand corrected. Thank you. -- http://mail.python.org/mailman/listinfo/python-list
Re: How to get an integer from a sequence of bytes
Am 30.05.2013 21:22, schrieb Ned Batchelder: On 5/30/2013 2:26 PM, Mok-Kong Shen wrote: Am 27.05.2013 17:30, schrieb Ned Batchelder: On 5/27/2013 10:45 AM, Mok-Kong Shen wrote: From an int one can use to_bytes to get its individual bytes, but how can one reconstruct the int from the sequence of bytes? The next thing in the docs after int.to_bytes is int.from_bytes: http://docs.python.org/3.3/library/stdtypes.html#int.from_bytes I am sorry to have overlooked that. But one thing I yet wonder is why there is no direct possibilty of converting a byte to an int in [0,255], i.e. with a constrct int(b), where b is a byte. Presumably you want this to work: int(b'\x03') 3 But you also want this to work: int(b'7') 7 These two interpretations are incompatible. If b'\x03' becomes 3, then shouldn't b'\x37' become 55? But b'\x37' is b'7', and you want that to be 7. b'7' is the byte with the character 7 in a certain code, so that's ok. In other PLs one assigns an int to a byte, with that int in either decimal notation or hexadecimal notation, or else one assigns a character to it, in which case it gets the value of the character in a certain code. What I don't yet understand is why Python is apprently different from other PLs in that point in not allowing direct coersion of a byte to an int. M. K. Shen -- http://mail.python.org/mailman/listinfo/python-list
Re: How to get an integer from a sequence of bytes
On Mon, Jun 3, 2013 at 5:25 AM, Mok-Kong Shen mok-kong.s...@t-online.de wrote: b'7' is the byte with the character 7 in a certain code, so that's ok. In other PLs one assigns an int to a byte, with that int in either decimal notation or hexadecimal notation, or else one assigns a character to it, in which case it gets the value of the character in a certain code. What I don't yet understand is why Python is apprently different from other PLs in that point in not allowing direct coersion of a byte to an int. It does. Just subscript it: b'7'[0] 55 ChrisA -- http://mail.python.org/mailman/listinfo/python-list
Re: How to get an integer from a sequence of bytes
Am 27.05.2013 17:30, schrieb Ned Batchelder: On 5/27/2013 10:45 AM, Mok-Kong Shen wrote: From an int one can use to_bytes to get its individual bytes, but how can one reconstruct the int from the sequence of bytes? The next thing in the docs after int.to_bytes is int.from_bytes: http://docs.python.org/3.3/library/stdtypes.html#int.from_bytes I am sorry to have overlooked that. But one thing I yet wonder is why there is no direct possibilty of converting a byte to an int in [0,255], i.e. with a constrct int(b), where b is a byte. M. K. Shen -- http://mail.python.org/mailman/listinfo/python-list
Re: How to get an integer from a sequence of bytes
On Thu, May 30, 2013 at 12:26 PM, Mok-Kong Shen mok-kong.s...@t-online.de wrote: Am 27.05.2013 17:30, schrieb Ned Batchelder: On 5/27/2013 10:45 AM, Mok-Kong Shen wrote: From an int one can use to_bytes to get its individual bytes, but how can one reconstruct the int from the sequence of bytes? The next thing in the docs after int.to_bytes is int.from_bytes: http://docs.python.org/3.3/library/stdtypes.html#int.from_bytes I am sorry to have overlooked that. But one thing I yet wonder is why there is no direct possibilty of converting a byte to an int in [0,255], i.e. with a constrct int(b), where b is a byte. The bytes object can be viewed as a sequence of ints. So if b is a bytes object of non-zero length, then b[0] is an int in range(0, 256). -- http://mail.python.org/mailman/listinfo/python-list
Re: How to get an integer from a sequence of bytes
On 30 mai, 20:42, Ian Kelly ian.g.ke...@gmail.com wrote:
On Thu, May 30, 2013 at 12:26 PM, Mok-Kong Shen
mok-kong.s...@t-online.de wrote:
Am 27.05.2013 17:30, schrieb Ned Batchelder:
On 5/27/2013 10:45 AM, Mok-Kong Shen wrote:
From an int one can use to_bytes to get its individual bytes,
but how can one reconstruct the int from the sequence of bytes?
The next thing in the docs after int.to_bytes is int.from_bytes:
http://docs.python.org/3.3/library/stdtypes.html#int.from_bytes
I am sorry to have overlooked that. But one thing I yet wonder is why
there is no direct possibilty of converting a byte to an int in [0,255],
i.e. with a constrct int(b), where b is a byte.
The bytes object can be viewed as a sequence of ints. So if b is a
bytes object of non-zero length, then b[0] is an int in range(0, 256).
Well, Python now speaks only integer, the rest is
commodity and there is a good coherency.
bin(255)
'0b'
oct(255)
'0o377'
255
255
hex(255)
'0xff'
int('0b', 2)
255
int('0o377', 8)
255
int('255')
255
int('0xff', 16)
255
0b
255
0o377
255
255
255
0xff
255
type(0b)
class 'int'
type(0o377)
class 'int'
type(255)
class 'int'
type(0xff)
class 'int'
jmf
--
http://mail.python.org/mailman/listinfo/python-list
Re: How to get an integer from a sequence of bytes
On 5/30/2013 2:26 PM, Mok-Kong Shen wrote: Am 27.05.2013 17:30, schrieb Ned Batchelder: On 5/27/2013 10:45 AM, Mok-Kong Shen wrote: From an int one can use to_bytes to get its individual bytes, but how can one reconstruct the int from the sequence of bytes? The next thing in the docs after int.to_bytes is int.from_bytes: http://docs.python.org/3.3/library/stdtypes.html#int.from_bytes I am sorry to have overlooked that. But one thing I yet wonder is why there is no direct possibilty of converting a byte to an int in [0,255], i.e. with a constrct int(b), where b is a byte. Presumably you want this to work: int(b'\x03') 3 But you also want this to work: int(b'7') 7 These two interpretations are incompatible. If b'\x03' becomes 3, then shouldn't b'\x37' become 55? But b'\x37' is b'7', and you want that to be 7. --Ned. M. K. Shen -- http://mail.python.org/mailman/listinfo/python-list
Re: How to get an integer from a sequence of bytes
On 2013-05-27, Mok-Kong Shen mok-kong.s...@t-online.de wrote: From an int one can use to_bytes to get its individual bytes, but how can one reconstruct the int from the sequence of bytes? One way is using the struct module. -- Grant Edwards grant.b.edwardsYow! Uh-oh!! I forgot at to submit to COMPULSORY gmail.comURINALYSIS! -- http://mail.python.org/mailman/listinfo/python-list
Re: How to get an integer from a sequence of bytes
On Mon, 27 May 2013 16:45:05 +0200, Mok-Kong Shen wrote: From an int one can use to_bytes to get its individual bytes, but how can one reconstruct the int from the sequence of bytes? Here's one way: py n = 11999102937234 py m = 0 py for b in n.to_bytes(6, 'big'): ... m = 256*m + b ... py m == n True -- Steven -- http://mail.python.org/mailman/listinfo/python-list
Re: How to get an integer from a sequence of bytes
On 5/27/2013 10:45 AM, Mok-Kong Shen wrote: From an int one can use to_bytes to get its individual bytes, but how can one reconstruct the int from the sequence of bytes? The next thing in the docs after int.to_bytes is int.from_bytes: http://docs.python.org/3.3/library/stdtypes.html#int.from_bytes --Ned. Thanks in advance. M. K. Shen -- http://mail.python.org/mailman/listinfo/python-list
Re: How to get an integer from a sequence of bytes
On Mon, 27 May 2013 11:30:18 -0400, Ned Batchelder wrote: On 5/27/2013 10:45 AM, Mok-Kong Shen wrote: From an int one can use to_bytes to get its individual bytes, but how can one reconstruct the int from the sequence of bytes? The next thing in the docs after int.to_bytes is int.from_bytes: And I can't believe I missed that too :-( -- Steven -- http://mail.python.org/mailman/listinfo/python-list
RE: How to get an integer from a sequence of bytes
From: steve+comp.lang.pyt...@pearwood.info Subject: Re: How to get an integer from a sequence of bytes Date: Mon, 27 May 2013 15:00:39 + To: python-list@python.org On Mon, 27 May 2013 16:45:05 +0200, Mok-Kong Shen wrote: From an int one can use to_bytes to get its individual bytes, but how can one reconstruct the int from the sequence of bytes? Here's one way: py n = 11999102937234 py m = 0 py for b in n.to_bytes(6, 'big'): ... m = 256*m + b ... py m == n True -- Steven -- http://mail.python.org/mailman/listinfo/python-list Python 2 doesn't have to_bytes()! :( # Python 2, LSB 1st def to_lil_bytes(x): r = [] while x != 0: r.append(int(x 0b)) x= 8 return r # Python 2, LSB 1st def from_lil_bytes(l): x = 0 for i in range(len(l)-1, -1, -1): x = 8 x |= l[i] return x # Python 2, MSB 1st def to_big_bytes(x): r = [] while x != 0: r.insert(0, int(x 0b)) x= 8 return r # Python 2, MSB 1st def from_big_bytes(l): x = 0 for i in range(len(l)): x = 8 x |= l[i] return x Can it be faster? -- http://mail.python.org/mailman/listinfo/python-list
Re: How to get an integer from a sequence of bytes
On 05/27/2013 08:31 PM, Steven D'Aprano wrote: On Mon, 27 May 2013 11:30:18 -0400, Ned Batchelder wrote: On 5/27/2013 10:45 AM, Mok-Kong Shen wrote: From an int one can use to_bytes to get its individual bytes, but how can one reconstruct the int from the sequence of bytes? The next thing in the docs after int.to_bytes is int.from_bytes: And I can't believe I missed that too :-( And that approach probably works for negative ints too. -- DaveA -- http://mail.python.org/mailman/listinfo/python-list
