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dax_scan_value(3dax)
dax_scan_value(3DAX) DAX Library Functions dax_scan_value(3DAX)
NAME
dax_scan_value - compare vector elements with a specified value
SYNOPSIS
cc [ flag... ] file... -ldax [ library...]
#include <dax.h>
dax_result_t
dax_scan_value(dax_context_t *ctx, uint64_t flags,
dax_vec_t *src, dax_vec_t *dst, dax_compare_t op, dax_int_t *val);
DESCRIPTION
This function compares each element of src to a single value by using
the operation specified in op. If an element in src matches the user
specified value, the corresponding bit in the dst vector is set to 1
else set to 0. All values are unsigned, with the most significant bit
(MSB) on the left and decreasing bit significance moving to the right
within a byte and to the next higher address byte.
If src is zipped, translates each code word of src by using the src
codec and produces a 1 to 8 byte symbol which it appends to an interme‐
diate unzip stream. It then partitions the unzip stream into elements
at src->elem_width boundaries, repeats each element if src is run-
length encoded, and compares it with val.
In a variable width src, the i^th element of the src->aux_data field
gives the width of the i^th unzipped element.
In a run-length encoded src, the i^th element of the src->aux_data
field gives the repeat count of the i^th unzipped element as described
in the dax_vec_t(3DAX) man page. The aux_data field is not in zipped
form.
The op parameter can be set to any one of the following values:
DAX_EQ element == value
DAX_NE element != value
DAX_LT element < value
DAX_LE element <= value
DAX_GT element > value
DAX_GE element >= value
The src element width can be:
o 1 to 16 bits or 1 to 16 bytes in libdax version 1
o 1 to 24 bits or 1 to 16 bytes in libdax version 2
The src format may be fixed width, variable width, or run-length en‐
coded.
The val argument contains a comparison value that is:
o 1 to 16 bits or 1 to 16 bytes wide in libdax version 1
o 1 to 24 bits or 1 to 16 bytes wide in libdax version 2
val has the following structure:
typedef struct {
uint32_t format;
uint32_t elem_width;
uint64_t dword[3];
} dax_int_t;
dword[0] is the high order word, dword[1] is the middle order word, and
dword[2] is the low order word. Each word is big endian. The width of
the value is given by elem_width, in units of bits if (format &
DAX_BITS), else in units of bytes. The high order bytes above
elem_width within the partially used dwords must be 0. Checks this con‐
dition only if the DAX_DEBUG_EXTRA debug option is set. Ignores the
high order dwords that are above elem_width. For a fixed-width src, the
elem_width value must match the width of the src element.
Note -
libdax versions 1 and 2 do not use dword[0].
The following rules apply when comparing two values that have different
widths:
o Each value is round up to a byte-sized boundary, padded with
0 bits at the MSB as needed.
o If the rounded widths are the same, apply normal comparison
rules.
o If the rounded widths differ, the values are not equal.
o Compares the left most bytes by using the normal rules
up to the width of the shorter value. If they match, the
shorter element is smaller.
The dst->offset field must be set to 0.
If you omit the DAX_ONES_INDEX flag, the width of the elements in dst
must be 1 bit and the number of elements in dst must be at least the
number of elements in src. The latter number includes expansion from
run-length encoding. If src is run-length encoded, this condition is
only checked if the DAX_DEBUG_EXTRA debug option is set. The data in
dst must start on a 64 byte boundary. You must round up the size of the
data in dst as described in the dax_vec_t(3DAX) man page.
The following address ranges must not overlap:
o Address range of the src->data vector and the dst->data vec‐
tor.
o Address range of the src->aux_data vector and the dst->data
vector.
The libdax library checks the overlap in the address ranges only if the
DAX_DEBUG_EXTRA debug option is set. If violations of the conditions
occur and are not checked, you will get undefined results.
Supported Flags
The flags parameter can be set to one or more following values:
DAX_ONES_INDEX Instead of writing a single 0 or 1 bit to dst for
each element in src, write the index of the src ele‐
ment for which the translation is 1. The indices
start at 0. The width of the elements in dst may be 2
or 4 bytes, and correspondingly writes each index as
a 2 or 4-byte big-endian word. If the index is too
large for the word, writes the maximum unsigned value
for the word in libdax versions 1 and 2. The number
of elements in dst must be at least the number of el‐
ements that translate to 1. If this is not known, use
the number of elements in src as an upper bound.
Limits the number of elements in src to 2^32 when you
specify this flag.
DAX_CACHE_DST Writes results to cache. If not specified, invali‐
dates the address range for dst in the cache, and
writes the result to the main memory.
DAX_NOWAIT If the DAX command queue is full, returns without
submitting the command, instead of waiting to submit.
RETURN VALUES
Returns the number of matching elements in the dax_result_t count field
and sets the dax_result_t status field to one of the following values:
DAX_SUCCESS Operation completed successfully
DAX_EINVAL Invalid argument, detected by libdax
DAX_EPARSE Invalid argument, detected by DAX
DAX_EDATAFMT The true value of an aux_data element is 0, or the
width of a zip symbol is less than 1 or greater than
8, detected by DAX.
DAX_EOVERFLOW Output buffer overflow
DAX_EADI ADI mismatch error for an input or output buffer
DAX_ETHREAD The calling thread did not create ctx
DAX_EBUSY DAX is busy and nowait was requested
DAX_EINTERNAL Unknown internal error. Caller must stop using ctx.
EXAMPLES
The following examples show comparisons between elements with different
widths. Each expression below is true.
o "4" > "3"
o "4" > "33"
o "4" > "04"
o "4" < "40"
USAGE
The DAX_CACHE_DST flag generally improves performance if the size of
the results is small relative to the cachesize, and the program uses
the data soon after the function completes. It may reduce performance
if the result is large and displaces other useful data from the cache.
The DAX_ONES_INDEX flag improves performance if the selectivity of the
scan is low, which means that a small percentage of src elements pro‐
duce the comparison result as true. The size of dst in bytes can be
smaller, and software can efficiently select the elements in src by us‐
ing the indices. When you use a 4-byte index, the dst size is smaller
if selectivity is less than 1/32. But if selectivity is 100%, the size
of dst is 32 times larger with DAX_ONES_INDEX.
ATTRIBUTES
See attributes(7) for descriptions of the following attributes:
tab() box; cw(2.75i) |cw(2.75i) lw(2.75i) |lw(2.75i) ATTRIBUTE TYPEAT‐
TRIBUTE VALUE _ Availabilitysystem/library _ Interface StabilityCommit‐
ted
SEE ALSO
libdax(3LIB), dax_vec_t(3DAX), dax_adi(3DAX), dax_dtrace(3DAX),
dax_int_create(3DAX), dax_zip(3DAX)
Oracle Solaris 11.4 03 Mar 2017 dax_scan_value(3DAX)