common/include/nextnonzero.h

   1 /* nbdkit
   2  * Copyright Red Hat
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   4  * Redistribution and use in source and binary forms, with or without
   5  * modification, are permitted provided that the following conditions are
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  11  * * Redistributions in binary form must reproduce the above copyright
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  13  * documentation and/or other materials provided with the distribution.
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  16  * used to endorse or promote products derived from this software without
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  18  *
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  22  * PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR
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  31  */
  32
  33 #ifndef NBDKIT_NEXTNONZERO_H
  34 #define NBDKIT_NEXTNONZERO_H
  35
  36 /* Given a byte buffer, return a pointer to the first non-zero byte,
  37  * or return NULL if we reach the end of the buffer.
  38  *
  39  * XXX: Even with -O3 -mavx2, gcc 8.2.1 does a terrible job with this
  40  * loop, compiling it completely naively.  QEMU has an AVX2
  41  * implementation of a similar loop.
  42  *
  43  * See also:
  44  * https://sourceware.org/bugzilla/show_bug.cgi?id=19920
  45  * https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69908
  46  */
  47 static inline const char * __attribute__ ((__nonnull__ (1)))
  48 next_non_zero (const char *buffer, size_t size)
  49 {
  50   size_t i;
  51
  52   for (i = 0; i < size; ++i)
  53     if (buffer[i] != 0)
  54       return &buffer[i];
  55   return NULL;
  56 }
  57
  58 #endif /* NBDKIT_NEXTNONZERO_H */