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      1 /*
      2  * Copyright (C) 2015 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 //#define LOG_NDEBUG 0
     18 #define LOG_TAG "audio_utils_fifo"
     19 
     20 #include <stdlib.h>
     21 #include <string.h>
     22 #include <audio_utils/fifo.h>
     23 #include <audio_utils/roundup.h>
     24 #include <cutils/atomic.h>
     25 #include <cutils/log.h>
     26 
     27 void audio_utils_fifo_init(struct audio_utils_fifo *fifo, size_t frameCount, size_t frameSize,
     28         void *buffer)
     29 {
     30     // We would need a 64-bit roundup to support larger frameCount.
     31     ALOG_ASSERT(fifo != NULL && frameCount > 0 && frameSize > 0 && buffer != NULL);
     32     fifo->mFrameCount = frameCount;
     33     fifo->mFrameCountP2 = roundup(frameCount);
     34     fifo->mFudgeFactor = fifo->mFrameCountP2 - fifo->mFrameCount;
     35     fifo->mFrameSize = frameSize;
     36     fifo->mBuffer = buffer;
     37     fifo->mFront = 0;
     38     fifo->mRear = 0;
     39 }
     40 
     41 void audio_utils_fifo_deinit(struct audio_utils_fifo *fifo __unused)
     42 {
     43 }
     44 
     45 // Return a new index as the sum of an old index (either mFront or mRear) and a specified increment.
     46 static inline int32_t audio_utils_fifo_sum(struct audio_utils_fifo *fifo, int32_t index,
     47         uint32_t increment)
     48 {
     49     if (fifo->mFudgeFactor) {
     50         uint32_t mask = fifo->mFrameCountP2 - 1;
     51         ALOG_ASSERT((index & mask) < fifo->mFrameCount);
     52         ALOG_ASSERT(/*0 <= increment &&*/ increment <= fifo->mFrameCountP2);
     53         if ((index & mask) + increment >= fifo->mFrameCount) {
     54             increment += fifo->mFudgeFactor;
     55         }
     56         index += increment;
     57         ALOG_ASSERT((index & mask) < fifo->mFrameCount);
     58         return index;
     59     } else {
     60         return index + increment;
     61     }
     62 }
     63 
     64 // Return the difference between two indices: rear - front, where 0 <= difference <= mFrameCount.
     65 static inline size_t audio_utils_fifo_diff(struct audio_utils_fifo *fifo, int32_t rear,
     66         int32_t front)
     67 {
     68     int32_t diff = rear - front;
     69     if (fifo->mFudgeFactor) {
     70         uint32_t mask = ~(fifo->mFrameCountP2 - 1);
     71         int32_t genDiff = (rear & mask) - (front & mask);
     72         if (genDiff != 0) {
     73             ALOG_ASSERT(genDiff == (int32_t) fifo->mFrameCountP2);
     74             diff -= fifo->mFudgeFactor;
     75         }
     76     }
     77     // FIFO should not be overfull
     78     ALOG_ASSERT(0 <= diff && diff <= (int32_t) fifo->mFrameCount);
     79     return (size_t) diff;
     80 }
     81 
     82 ssize_t audio_utils_fifo_write(struct audio_utils_fifo *fifo, const void *buffer, size_t count)
     83 {
     84     int32_t front = android_atomic_acquire_load(&fifo->mFront);
     85     int32_t rear = fifo->mRear;
     86     size_t availToWrite = fifo->mFrameCount - audio_utils_fifo_diff(fifo, rear, front);
     87     if (availToWrite > count) {
     88         availToWrite = count;
     89     }
     90     rear &= fifo->mFrameCountP2 - 1;
     91     size_t part1 = fifo->mFrameCount - rear;
     92     if (part1 > availToWrite) {
     93         part1 = availToWrite;
     94     }
     95     if (part1 > 0) {
     96         memcpy((char *) fifo->mBuffer + (rear * fifo->mFrameSize), buffer,
     97                 part1 * fifo->mFrameSize);
     98         size_t part2 = availToWrite - part1;
     99         if (part2 > 0) {
    100             memcpy(fifo->mBuffer, (char *) buffer + (part1 * fifo->mFrameSize),
    101                     part2 * fifo->mFrameSize);
    102         }
    103         android_atomic_release_store(audio_utils_fifo_sum(fifo, fifo->mRear, availToWrite),
    104                 &fifo->mRear);
    105     }
    106     return availToWrite;
    107 }
    108 
    109 ssize_t audio_utils_fifo_read(struct audio_utils_fifo *fifo, void *buffer, size_t count)
    110 {
    111     int32_t rear = android_atomic_acquire_load(&fifo->mRear);
    112     int32_t front = fifo->mFront;
    113     size_t availToRead = audio_utils_fifo_diff(fifo, rear, front);
    114     if (availToRead > count) {
    115         availToRead = count;
    116     }
    117     front &= fifo->mFrameCountP2 - 1;
    118     size_t part1 = fifo->mFrameCount - front;
    119     if (part1 > availToRead) {
    120         part1 = availToRead;
    121     }
    122     if (part1 > 0) {
    123         memcpy(buffer, (char *) fifo->mBuffer + (front * fifo->mFrameSize),
    124                 part1 * fifo->mFrameSize);
    125         size_t part2 = availToRead - part1;
    126         if (part2 > 0) {
    127             memcpy((char *) buffer + (part1 * fifo->mFrameSize), fifo->mBuffer,
    128                     part2 * fifo->mFrameSize);
    129         }
    130         android_atomic_release_store(audio_utils_fifo_sum(fifo, fifo->mFront, availToRead),
    131                 &fifo->mFront);
    132     }
    133     return availToRead;
    134 }
    135