Hacker News new | past | comments | ask | show | jobs | submit login

So many to choose from ...

Convert single char c into an integer:

    int value = '0' - c;
Get the length of a static string you can use sizeof() instead of strlen()

    int len1 = sizeof("hello");   // compile-time string length
A fast and simple ring buffer (borrowed from Quake code)

    UPDATE_MASK = ARRAY_SIZE - 1;
    array[i++ & UPDATE_MASK] = data;
Init all bits of a mask to 1 on any architecture:

    unsigned int flags = -1;



I think you meant

    int value = c - '0';
Also, remember that sizeof("string") includes the null terminator while strlen() does not.


The ring buffer is a nice trick, but it only works on array sizes that are a multiple of 2. The generalized version would be "array[i++ % ARRAY_SIZE] = data". If ARRAY_SIZE happens to be a multiple of two, I'm sure most compilers would optimize to a bitmask anyways..


And if it is not a power of 2, the % operation will be anything but fast. If a size not a power of 2 is strictly required, a simple increment and compare is almost certainly faster.


Signed integer overflow is undefined, so make sure you're using an unsigned type in your ringbuffer example. (And an array with some-power-of-2 elements; you should probably use sizeof(array)/sizeof(<star> array) instead of ARRAY_SIZE too.)


If you want all-ones, shouldn't you just use ~0?


No. ~0 has type signed int, which on a one's complement machine is a negative zero. Converting this to an unsigned type yields zero. On a sign-magnitude machine, ~0 is -0x7fffffff (assuming 32-bit for simplicity). Conversion to unsigned 32-bit is done by adding 0x100000000, yielding 0x80000001, again not what was desired. If the variable being assigned to has a width different from that of int, things get even more interesting.


Ah. Thanks! Is there a ones-complement or sign-magnitude architecture still in production anywhere? (I'm curious; I have no idea.)


As far as I know analog devices still makes some ones-complement Analog to Digital Converters. But I don't know of any modern processor that uses them.


How about ~0U?


That will only set as many bits as are in an int, which is wrong if the type of the variable you are setting is wider than int. For a long, you could of course use ~0ul, and so on for other types, but then you'd have to find and update every such assignment if the variable were ever changed to a wider type.


I think you meant:

    int value = c - '0';
Otherwise, value will be negative.




Guidelines | FAQ | Lists | API | Security | Legal | Apply to YC | Contact

Search: