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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
u_vector_init(struct u_vector * vector,uint32_t element_size,uint32_t size)38 u_vector_init(struct u_vector *vector, uint32_t element_size, uint32_t size)
39 {
40    assert(util_is_power_of_two(size));
41    assert(element_size < size && util_is_power_of_two(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 *
u_vector_add(struct u_vector * vector)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 *
u_vector_remove(struct u_vector * vector)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 }
111