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cfilipov/bits.c

Created November 6, 2017 04:14
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Revisions

  1. cfilipov created this gist Nov 6, 2017.
    108 changes: 108 additions & 0 deletions bits.c
    View file
    Original file line number Diff line number Diff line change
    @@ -0,0 +1,108 @@
    #include "stdio.h"
    #include "stdint.h"

    /**
    * Print the binary representation of an integer `n` with length `len`.
    * Any unsigned integer can be safely cast to uintmax_t.
    *
    * Shift right then mask to the last bit.
    */
    void printb2(uintmax_t n, size_t len)
    {
    size_t w = len - 1;
    for (size_t i = 0; i < len; i++)
    printf("%ju ", (n >> (w - i)) & 0x01);
    }

    /**
    * Print the binary representation of an integer `n` with length `len`.
    * Any unsigned integer can be safely cast to uintmax_t.
    *
    * Start with a bit mask where the MSB is set then shift right until the LSB.
    */
    void printb3(uintmax_t n, size_t len)
    {
    /* Note the 1U is important because otherwise 1 will be treated as a
    * signed value, resulting in all the bits to the left being set. */
    for (uintmax_t i = 1U << (len - 1); i > 0; i >>= 1)
    printf("%i ", n & i ? 1 : 0);
    }

    /**
    * Print the binary representation of an integer `n` with length `len`.
    * Any unsigned integer can be safely cast to uintmax_t.
    *
    * Same as printb3, using `while` instead of `for`.
    */
    void printb4(uintmax_t n, size_t len)
    {
    while (--len < SIZE_MAX)
    printf("%i ", n & (1 << len) ? 1 : 0);
    }

    /**
    * Print the binary representation of an 8-bit wide integer.
    */
    void printb(uint8_t i)
    {
    printf("%x ", (i >> 7) & 0x01);
    printf("%x ", (i >> 6) & 0x01);
    printf("%x ", (i >> 5) & 0x01);
    printf("%x ", (i >> 4) & 0x01);
    printf("%x ", (i >> 3) & 0x01);
    printf("%x ", (i >> 2) & 0x01);
    printf("%x ", (i >> 1) & 0x01);
    printf("%x", (i >> 0) & 0x01);
    }

    /*
    Swap the second and fourth bytes in an integer sequence
    http://stackoverflow.com/questions/17409874
    See also: http://commandcenter.blogspot.com/2012/04
    int someInt = 0x12345678;
    int byte2 = someInt & 0x00FF0000;
    int byte4 = someInt & 0x000000FF;
    int swapd = (someInt & 0xFF00FF00) | (byte2 >> 16) | (byte4 << 16);
    byte2 = 0x00340000
    byte4 = 0x00000078
    someInt & 0xFF00FF00 = 0x12005600
    byte2 >> 16 = 0x00000034
    byte4 << 16 = 0x00780000
    0x12005600
    | 0x00000034
    | 0x00780000
    = 0x12785634
    */

    enum byte_order {
    BIG_ENDIAN,
    LITTLE_ENDIAN
    };

    enum byte_order get_byte_order() {

    }

    int main()
    {
    uint8_t i8 = 42;
    uint16_t i16 = 42;
    uint32_t i32 = 42;

    printf("b: "), printb(i8), printf("\n");
    printf("b2: "), printb2(i8, 8), printf("\n");
    printf("b3: "), printb3(i8, 8), printf("\n");
    printf("b4: "), printb4(i8, 8), printf("\n\n");
    printf("b2: "), printb2(i16, 16), printf("\n");
    printf("b3: "), printb3(i16, 16), printf("\n");
    printf("b4: "), printb4(i16, 16), printf("\n\n");
    printf("b2: "), printb2(i32, 32), printf("\n");
    printf("b3: "), printb3(i32, 32), printf("\n");
    printf("b4: "), printb4(i32, 32), printf("\n");

    return 0;
    }