BITPOS

BITPOS key bit [range]

Available since

2.8.7

Time complexity

O(N)

ACL categories

@read, @bitmap, @slow

Return the position of the first bit set to 1 or 0 in a string.

The position is returned, thinking of the string as an array of bits from left to right, where the first byte’s most significant bit is at position 0, the second byte’s most significant bit is at position 8, and so forth.

The same bit position convention is followed by GETBIT and SETBIT.

By default, all the bytes contained in the string are examined. It is possible to look for bits only in a specified interval passing the additional arguments start and end (it is possible to just pass start, the operation will assume that the end is the last byte of the string. However there are semantic differences as explained later). By default, the range is interpreted as a range of bytes and not a range of bits, so start=0 and end=2 means to look at the first three bytes.

You can use the optional BIT modifier to specify that the range should be interpreted as a range of bits. So start=0 and end=2 means to look at the first three bits.

Note that bit positions are returned always as absolute values starting from bit zero even when start and end are used to specify a range.

Like for the GETRANGE command start and end can contain negative values in order to index bytes starting from the end of the string, where -1 is the last byte, -2 is the penultimate, and so forth. When BIT is specified, -1 is the last bit, -2 is the penultimate, and so forth.

Non-existent keys are treated as empty strings.

Examples #

SET mykey "\xff\xf0\x00"
BITPOS mykey 0
SET mykey "\x00\xff\xf0"
BITPOS mykey 1 0
BITPOS mykey 1 2
BITPOS mykey 1 2 -1 BYTE
BITPOS mykey 1 7 15 BIT
set mykey "\x00\x00\x00"
BITPOS mykey 1
BITPOS mykey 1 7 -3 BIT

History #

7.0.0

Added the `BYTE|BIT` option.