bitops.c

#include <string.h>
#include <stdlib.h>
#include <stdio.h>
#include <assert.h>
#include <limits.h>

#include "redis.h"
#include "commondef.h"
#include "commonfunc.h"
#include "zmalloc.h"
#include "object.h"
#include "sds.h"
#include "db.h"
#include "util.h"

/* Count number of bits set in the binary array pointed by 's' and long
 * 'count' bytes. The implementation of this function is required to
 * work with a input string length up to 512 MB. */
size_t redisPopcount(void *s, long count) {
    size_t bits = 0;
    unsigned char *p = s;
    uint32_t *p4;
    static const unsigned char bitsinbyte[256] = {0,1,1,2,1,2,2,3,1,2,2,3,2,3,3,4,1,2,2,3,2,3,3,4,2,3,3,4,3,4,4,5,1,2,2,3,2,3,3,4,2,3,3,4,3,4,4,5,2,3,3,4,3,4,4,5,3,4,4,5,4,5,5,6,1,2,2,3,2,3,3,4,2,3,3,4,3,4,4,5,2,3,3,4,3,4,4,5,3,4,4,5,4,5,5,6,2,3,3,4,3,4,4,5,3,4,4,5,4,5,5,6,3,4,4,5,4,5,5,6,4,5,5,6,5,6,6,7,1,2,2,3,2,3,3,4,2,3,3,4,3,4,4,5,2,3,3,4,3,4,4,5,3,4,4,5,4,5,5,6,2,3,3,4,3,4,4,5,3,4,4,5,4,5,5,6,3,4,4,5,4,5,5,6,4,5,5,6,5,6,6,7,2,3,3,4,3,4,4,5,3,4,4,5,4,5,5,6,3,4,4,5,4,5,5,6,4,5,5,6,5,6,6,7,3,4,4,5,4,5,5,6,4,5,5,6,5,6,6,7,4,5,5,6,5,6,6,7,5,6,6,7,6,7,7,8};

    /* Count initial bytes not aligned to 32 bit. */
    while((unsigned long)p & 3 && count) {
        bits += bitsinbyte[*p++];
        count--;
    }

    /* Count bits 28 bytes at a time */
    p4 = (uint32_t*)p;
    while(count>=28) {
        uint32_t aux1, aux2, aux3, aux4, aux5, aux6, aux7;

        aux1 = *p4++;
        aux2 = *p4++;
        aux3 = *p4++;
        aux4 = *p4++;
        aux5 = *p4++;
        aux6 = *p4++;
        aux7 = *p4++;
        count -= 28;

        aux1 = aux1 - ((aux1 >> 1) & 0x55555555);
        aux1 = (aux1 & 0x33333333) + ((aux1 >> 2) & 0x33333333);
        aux2 = aux2 - ((aux2 >> 1) & 0x55555555);
        aux2 = (aux2 & 0x33333333) + ((aux2 >> 2) & 0x33333333);
        aux3 = aux3 - ((aux3 >> 1) & 0x55555555);
        aux3 = (aux3 & 0x33333333) + ((aux3 >> 2) & 0x33333333);
        aux4 = aux4 - ((aux4 >> 1) & 0x55555555);
        aux4 = (aux4 & 0x33333333) + ((aux4 >> 2) & 0x33333333);
        aux5 = aux5 - ((aux5 >> 1) & 0x55555555);
        aux5 = (aux5 & 0x33333333) + ((aux5 >> 2) & 0x33333333);
        aux6 = aux6 - ((aux6 >> 1) & 0x55555555);
        aux6 = (aux6 & 0x33333333) + ((aux6 >> 2) & 0x33333333);
        aux7 = aux7 - ((aux7 >> 1) & 0x55555555);
        aux7 = (aux7 & 0x33333333) + ((aux7 >> 2) & 0x33333333);
        bits += ((((aux1 + (aux1 >> 4)) & 0x0F0F0F0F) +
                    ((aux2 + (aux2 >> 4)) & 0x0F0F0F0F) +
                    ((aux3 + (aux3 >> 4)) & 0x0F0F0F0F) +
                    ((aux4 + (aux4 >> 4)) & 0x0F0F0F0F) +
                    ((aux5 + (aux5 >> 4)) & 0x0F0F0F0F) +
                    ((aux6 + (aux6 >> 4)) & 0x0F0F0F0F) +
                    ((aux7 + (aux7 >> 4)) & 0x0F0F0F0F))* 0x01010101) >> 24;
    }
    /* Count the remaining bytes. */
    p = (unsigned char*)p4;
    while(count--) bits += bitsinbyte[*p++];
    return bits;
}

/* Return the position of the first bit set to one (if 'bit' is 1) or
 * zero (if 'bit' is 0) in the bitmap starting at 's' and long 'count' bytes.
 *
 * The function is guaranteed to return a value >= 0 if 'bit' is 0 since if
 * no zero bit is found, it returns count*8 assuming the string is zero
 * padded on the right. However if 'bit' is 1 it is possible that there is
 * not a single set bit in the bitmap. In this special case -1 is returned. */
long redisBitpos(void *s, unsigned long count, int bit) {
    unsigned long *l;
    unsigned char *c;
    unsigned long skipval, word = 0, one;
    long pos = 0; /* Position of bit, to return to the caller. */
    unsigned long j;
    int found;

    /* Process whole words first, seeking for first word that is not
     * all ones or all zeros respectively if we are lookig for zeros
     * or ones. This is much faster with large strings having contiguous
     * blocks of 1 or 0 bits compared to the vanilla bit per bit processing.
     *
     * Note that if we start from an address that is not aligned
     * to sizeof(unsigned long) we consume it byte by byte until it is
     * aligned. */

    /* Skip initial bits not aligned to sizeof(unsigned long) byte by byte. */
    skipval = bit ? 0 : UCHAR_MAX;
    c = (unsigned char*) s;
    found = 0;
    while((unsigned long)c & (sizeof(*l)-1) && count) {
        if (*c != skipval) {
            found = 1;
            break;
        }
        c++;
        count--;
        pos += 8;
    }

    /* Skip bits with full word step. */
    l = (unsigned long*) c;
    if (!found) {
        skipval = bit ? 0 : ULONG_MAX;
        while (count >= sizeof(*l)) {
            if (*l != skipval) break;
            l++;
            count -= sizeof(*l);
            pos += sizeof(*l)*8;
        }
    }

    /* Load bytes into "word" considering the first byte as the most significant
     * (we basically consider it as written in big endian, since we consider the
     * string as a set of bits from left to right, with the first bit at position
     * zero.
     *
     * Note that the loading is designed to work even when the bytes left
     * (count) are less than a full word. We pad it with zero on the right. */
    c = (unsigned char*)l;
    for (j = 0; j < sizeof(*l); j++) {
        word <<= 8;
        if (count) {
            word |= *c;
            c++;
            count--;
        }
    }

    /* Special case:
     * If bits in the string are all zero and we are looking for one,
     * return -1 to signal that there is not a single "1" in the whole
     * string. This can't happen when we are looking for "0" as we assume
     * that the right of the string is zero padded. */
    if (bit == 1 && word == 0) return -1;

    /* Last word left, scan bit by bit. The first thing we need is to
     * have a single "1" set in the most significant position in an
     * unsigned long. We don't know the size of the long so we use a
     * simple trick. */
    one = ULONG_MAX; /* All bits set to 1.*/
    one >>= 1;       /* All bits set to 1 but the MSB. */
    one = ~one;      /* All bits set to 0 but the MSB. */

    while(one) {
        if (((one & word) != 0) == bit) return pos;
        pos++;
        one >>= 1;
    }

    /* If we reached this point, there is a bug in the algorithm, since
     * the case of no match is handled as a special case before. */
    // serverPanic("End of redisBitpos() reached.");
    return 0; /* Just to avoid warnings. */
}

/* This is an helper function for commands implementations that need to write
 * bits to a string object. The command creates or pad with zeroes the string
 * so that the 'maxbit' bit can be addressed. The object is finally
 * returned. Otherwise if the key holds a wrong type NULL is returned and
 * an error is sent to the client. */
robj *lookupStringForBitCommand(redisDb *redis_db, robj *kobj, size_t maxbit) {
    size_t byte = maxbit >> 3;
    robj *o = lookupKeyWrite(redis_db,kobj);

    if (o == NULL) {
        o = createObject(OBJ_STRING,sdsnewlen(NULL, byte+1));
        dbAdd(redis_db,kobj,o);
    } else {
        if (checkType(o,OBJ_STRING)) return NULL;
        o = dbUnshareStringValue(redis_db,kobj,o);
        o->ptr = sdsgrowzero(o->ptr,byte+1);
    }
    return o;
}

/* Return a pointer to the string object content, and stores its length
 * in 'len'. The user is required to pass (likely stack allocated) buffer
 * 'llbuf' of at least LONG_STR_SIZE bytes. Such a buffer is used in the case
 * the object is integer encoded in order to provide the representation
 * without usign heap allocation.
 *
 * The function returns the pointer to the object array of bytes representing
 * the string it contains, that may be a pointer to 'llbuf' or to the
 * internal object representation. As a side effect 'len' is filled with
 * the length of such buffer.
 *
 * If the source object is NULL the function is guaranteed to return NULL
 * and set 'len' to 0. */
unsigned char *getObjectReadOnlyString(robj *o, long *len, char *llbuf) {
    assert(o->type == OBJ_STRING);
    unsigned char *p = NULL;

    /* Set the 'p' pointer to the string, that can be just a stack allocated
     * array if our string was integer encoded. */
    if (o && o->encoding == OBJ_ENCODING_INT) {
        p = (unsigned char*) llbuf;
        if (len) *len = ll2string(llbuf,LONG_STR_SIZE,(long)o->ptr);
    } else if (o) {
        p = (unsigned char*) o->ptr;
        if (len) *len = sdslen(o->ptr);
    } else {
        if (len) *len = 0;
    }
    return p;
}

int RcSetBit(redisCache db, robj *key, size_t bitoffset, long on)
{
    if (NULL == db || NULL == key) {
        return REDIS_INVALID_ARG;
    }
    redisDb *redis_db = (redisDb*)db;

    /* Bits can only be set or cleared... */
    if (on & ~1) {
        return C_ERR;
    }

    robj *o;
    if ((o = lookupStringForBitCommand(redis_db,key,bitoffset)) == NULL) {
        return C_ERR;
    }

    ssize_t byte, bit;
    int byteval;

    /* Get current values */
    byte = bitoffset >> 3;
    byteval = ((uint8_t*)o->ptr)[byte];
    bit = 7 - (bitoffset & 0x7);

    /* Update byte with new bit value and return original value */
    byteval &= ~(1 << bit);
    byteval |= ((on & 0x1) << bit);
    ((uint8_t*)o->ptr)[byte] = byteval;

    return C_OK;
}

int RcGetBit(redisCache db, robj *key, size_t bitoffset, long *val)
{
    if (NULL == db || NULL == key) {
        return REDIS_INVALID_ARG;
    }
    redisDb *redis_db = (redisDb*)db;

    robj *o;
    if ((o = lookupKeyRead(redis_db,key)) == NULL || checkType(o,OBJ_STRING)) {
        return REDIS_KEY_NOT_EXIST;
    }

    char llbuf[32];
    size_t byte, bit;
    size_t bitval = 0;

    byte = bitoffset >> 3;
    bit = 7 - (bitoffset & 0x7);
    if (sdsEncodedObject(o)) {
        if (byte < sdslen(o->ptr))
            bitval = ((uint8_t*)o->ptr)[byte] & (1 << bit);
    } else {
        if (byte < (size_t)ll2string(llbuf,sizeof(llbuf),(long)o->ptr))
            bitval = llbuf[byte] & (1 << bit);
    }

    *val = bitval ? 1 : 0;

    return C_OK;
}

int RcBitCount(redisCache db, robj *key, long start, long end, long *val, int have_offset)
{
    if (NULL == db || NULL == key) {
        return REDIS_INVALID_ARG;
    }
    redisDb *redis_db = (redisDb*)db;

    robj *o;
    if ((o = lookupKeyRead(redis_db,key)) == NULL || checkType(o,OBJ_STRING)) {
        return REDIS_KEY_NOT_EXIST;
    }

    /* Parse start/end range if any. */
    long strlen;
    char llbuf[LONG_STR_SIZE];
    unsigned char *p = getObjectReadOnlyString(o,&strlen,llbuf);
    if (have_offset) {
        /* Convert negative indexes */
        if (start < 0 && end < 0 && start > end) {
            return C_ERR;
        }
        if (start < 0) start = strlen+start;
        if (end < 0) end = strlen+end;
        if (start < 0) start = 0;
        if (end < 0) end = 0;
        if (end >= strlen) end = strlen-1;
    } else {
        /* The whole string. */
        start = 0;
        end = strlen-1;
    }

    /* Precondition: end >= 0 && end < strlen, so the only condition where
     * zero can be returned is: start > end. */
    if (start > end) {
        *val = 0;
    } else {
        long bytes = end-start+1;
        *val = redisPopcount(p+start,bytes);
    }

    return C_OK;
}

int RcBitPos(redisCache db, robj *key, long bit, long start, long end, long *val, int offset_status)
{
    if (NULL == db || NULL == key) {
        return REDIS_INVALID_ARG;
    }
    redisDb *redis_db = (redisDb*)db;

    if (bit != 0 && bit != 1) {
        return C_ERR;
    }

    robj *o;
    if ((o = lookupKeyRead(redis_db,key)) == NULL || checkType(o,OBJ_STRING)) {
        return REDIS_KEY_NOT_EXIST;
    }

    long strlen;
    char llbuf[LONG_STR_SIZE];
    int end_given = 0;
    unsigned char *p = getObjectReadOnlyString(o,&strlen,llbuf);
    /* Parse start/end range if any. */
    if (BIT_POS_START_OFFSET == offset_status
        || BIT_POS_START_END_OFFSET == offset_status) {

        if (BIT_POS_START_END_OFFSET == offset_status) {
            end_given = 1;
        } else {
            end = strlen-1;
        }
        /* Convert negative indexes */
        if (start < 0) start = strlen+start;
        if (end < 0) end = strlen+end;
        if (start < 0) start = 0;
        if (end < 0) end = 0;
        if (end >= strlen) end = strlen-1;
    } else if (BIT_POS_NO_OFFSET == offset_status) {
        /* The whole string. */
        start = 0;
        end = strlen-1;
    } else {
        /* Syntax error. */
        return C_ERR;
    }

    /* For empty ranges (start > end) we return -1 as an empty range does
     * not contain a 0 nor a 1. */
    if (start > end) {
        *val = -1;
    } else {
        long bytes = end-start+1;
        long pos = redisBitpos(p+start,bytes,bit);

        /* If we are looking for clear bits, and the user specified an exact
         * range with start-end, we can't consider the right of the range as
         * zero padded (as we do when no explicit end is given).
         *
         * So if redisBitpos() returns the first bit outside the range,
         * we return -1 to the caller, to mean, in the specified range there
         * is not a single "0" bit. */
        if (end_given && bit == 0 && pos == bytes*8) {
            *val = -1;
            return C_ERR;
        }
        if (pos != -1) pos += start*8; /* Adjust for the bytes we skipped. */
        *val = pos;
    }

    return C_OK;
}