Steve Litt wrote:
> On Fri, 24 Jun 2016 09:19:40 +0200
> Edward Bartolo <edb...@gmail.com> wrote:
>
> > Bitwise Operators:
> >
> > Pg 63:
> > /* getbits: get n bits from position p */
> >
> > unigned int getbits(unsigned int x, int p, int n)
> > {
> > return (x >> (p + 1 - n)) & ~(~0 << n);
> > }
>
> Stuff like this is the reason I soon abandoned K&R as a learning tool,
> and used it only to determine the official behavior of C.
>
> Bit stuffing, sliding and masking were a tool of the assembly programmer
> back when your RAM could be counted in four digits and your processor
> had little power. Using x, p and n instead of container_int,
> bit_position and bits_to_consider was relevant when computers were so
> anemic that shorter variable names made for faster compiles. And also,
> long variable names are difficult to format in a print book.
>
> In this day and age (and as a matter of fact since the early 1990's),
> packing bits into ints is usually premature optimization. It's usually
> better to malloc() 1024 ints whose values will be either 0 or 1 than
> to malloc() 64 its whose values go from 0 to 65535, and access
> individual bits. If RAM or performance later becomes an issue, THAT'S
> the time to bit-stuff and bit-manipulate.
>
> When K&R originally wrote their book in 1978, there were plenty of
> computers running magnetic core memory, and the language of system
> programmers was assembler. And early C didn't optimize that well. So of
> course they wrote their C with assembler idioms.
>
> I'd personally de-prioritize the bit arithmetic stuff. You can learn it
> at any time. The other thing I'd de-prioritize is the question mark
> operator: It's just (sometimes confusing) shorthand for what
> if/else if/else can do.
>
> Save your brainpower for pointers to functions. That's actually
> massively useful, and extremely difficult.
If it's about saving brainpower, a garbage-collected
scripting language is indicated. But this is a snark.
I looked at K&R in 1986, when I got my first PC clone,
and soon gave up in confusion.
Joel
> SteveT
>
> Steve Litt
> June 2016 featured book: Troubleshooting: Why Bother?
> http://www.troubleshooters.com/twb
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--
Joel Roth
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