src/util/u_vector.c

   1 /*
   2  * Copyright © 2015 Intel Corporation
   3  *
   4  * Permission is hereby granted, free of charge, to any person obtaining a
   5  * copy of this software and associated documentation files (the "Software"),
   6  * to deal in the Software without restriction, including without limitation
   7  * the rights to use, copy, modify, merge, publish, distribute, sublicense,
   8  * and/or sell copies of the Software, and to permit persons to whom the
   9  * Software is furnished to do so, subject to the following conditions:
  10  *
  11  * The above copyright notice and this permission notice (including the next
  12  * paragraph) shall be included in all copies or substantial portions of the
  13  * Software.
  14  *
  15  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  16  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  17  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
  18  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  19  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
  20  * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
  21  * IN THE SOFTWARE.
  22  */
  23
  24 #include <string.h>
  25 #include "util/u_math.h"
  26 #include "util/u_vector.h"
  27
  28 /** @file u_vector.c
  29  *
  30  * A dynamically growable, circular buffer.  Elements are added at head and
  31  * removed from tail. head and tail are free-running uint32_t indices and we
  32  * only compute the modulo with size when accessing the array.  This way,
  33  * number of bytes in the queue is always head - tail, even in case of
  34  * wraparound.
  35  */
  36
  37 int
  38 u_vector_init(struct u_vector *vector, uint32_t element_size, uint32_t size)
  39 {
  40    assert(util_is_power_of_two_nonzero(size));
  41    assert(element_size < size && util_is_power_of_two_nonzero(element_size));
  42
  43    vector->head = 0;
  44    vector->tail = 0;
  45    vector->element_size = element_size;
  46    vector->size = size;
  47    vector->data = malloc(size);
  48
  49    return vector->data != NULL;
  50 }
  51
  52 void *
  53 u_vector_add(struct u_vector *vector)
  54 {
  55    uint32_t offset, size, split, src_tail, dst_tail;
  56    void *data;
  57
  58    if (vector->head - vector->tail == vector->size) {
  59       size = vector->size * 2;
  60       data = malloc(size);
  61       if (data == NULL)
  62          return NULL;
  63       src_tail = vector->tail & (vector->size - 1);
  64       dst_tail = vector->tail & (size - 1);
  65       if (src_tail == 0) {
  66          /* Since we know that the vector is full, this means that it's
  67           * linear from start to end so we can do one copy.
  68           */
  69          memcpy((char *)data + dst_tail, vector->data, vector->size);
  70       } else {
  71          /* In this case, the vector is split into two pieces and we have
  72           * to do two copies.  We have to be careful to make sure each
  73           * piece goes to the right locations.  Thanks to the change in
  74           * size, it may or may not still wrap around.
  75           */
  76          split = u_align_u32(vector->tail, vector->size);
  77          assert(vector->tail <= split && split < vector->head);
  78          memcpy((char *)data + dst_tail, (char *)vector->data + src_tail,
  79                 split - vector->tail);
  80          memcpy((char *)data + (split & (size - 1)), vector->data,
  81                 vector->head - split);
  82       }
  83       free(vector->data);
  84       vector->data = data;
  85       vector->size = size;
  86    }
  87
  88    assert(vector->head - vector->tail < vector->size);
  89
  90    offset = vector->head & (vector->size - 1);
  91    vector->head += vector->element_size;
  92
  93    return (char *)vector->data + offset;
  94 }
  95
  96 void *
  97 u_vector_remove(struct u_vector *vector)
  98 {
  99    uint32_t offset;
 100
 101    if (vector->head == vector->tail)
 102       return NULL;
 103
 104    assert(vector->head - vector->tail <= vector->size);
 105
 106    offset = vector->tail & (vector->size - 1);
 107    vector->tail += vector->element_size;
 108
 109    return (char *)vector->data + offset;
 110 }