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// This code makes some assumptions on the implementation of
// base64_stream_encode_init(), base64_stream_encode() and base64_stream_decode().
// Basically these assumptions boil down to that when breaking the src into
// parts, out parts can be written without side effects.
// This is met when:
// 1) base64_stream_encode() and base64_stream_decode() don't use globals;
// 2) the shared variables src and out are not read or written outside of the
// bounds of their parts, i.e. when base64_stream_encode() reads a multiple
// of 3 bytes, it must write no more then a multiple of 4 bytes, not even
// temporarily;
// 3) the state flag can be discarded after base64_stream_encode() and
// base64_stream_decode() on the parts.
static inline void
base64_encode_openmp
( const char *src
, size_t srclen
, char *out
, size_t *outlen
, int flags
)
{
size_t s;
size_t t;
size_t sum = 0, len, last_len;
struct base64_state state, initial_state;
int num_threads, i;
// Request a number of threads but not necessarily get them:
#pragma omp parallel
{
// Get the number of threads used from one thread only,
// as num_threads is a shared var:
#pragma omp single
{
num_threads = omp_get_num_threads();
// Split the input string into num_threads parts, each
// part a multiple of 3 bytes. The remaining bytes will
// be done later:
len = srclen / (num_threads * 3);
len *= 3;
last_len = srclen - num_threads * len;
// Init the stream reader:
base64_stream_encode_init(&state, flags);
initial_state = state;
}
// Single has an implicit barrier for all threads to wait here
// for the above to complete:
#pragma omp for firstprivate(state) private(s) reduction(+:sum) schedule(static,1)
for (i = 0; i < num_threads; i++)
{
// Feed each part of the string to the stream reader:
base64_stream_encode(&state, src + i * len, len, out + i * len * 4 / 3, &s);
sum += s;
}
}
// As encoding should never fail and we encode an exact multiple
// of 3 bytes, we can discard state:
state = initial_state;
// Encode the remaining bytes:
base64_stream_encode(&state, src + num_threads * len, last_len, out + num_threads * len * 4 / 3, &s);
// Finalize the stream by writing trailer if any:
base64_stream_encode_final(&state, out + num_threads * len * 4 / 3 + s, &t);
// Final output length is stream length plus tail:
sum += s + t;
*outlen = sum;
}
static inline int
base64_decode_openmp
( const char *src
, size_t srclen
, char *out
, size_t *outlen
, int flags
)
{
int num_threads, result = 0, i;
size_t sum = 0, len, last_len, s;
struct base64_state state, initial_state;
// Request a number of threads but not necessarily get them:
#pragma omp parallel
{
// Get the number of threads used from one thread only,
// as num_threads is a shared var:
#pragma omp single
{
num_threads = omp_get_num_threads();
// Split the input string into num_threads parts, each
// part a multiple of 4 bytes. The remaining bytes will
// be done later:
len = srclen / (num_threads * 4);
len *= 4;
last_len = srclen - num_threads * len;
// Init the stream reader:
base64_stream_decode_init(&state, flags);
initial_state = state;
}
// Single has an implicit barrier to wait here for the above to
// complete:
#pragma omp for firstprivate(state) private(s) reduction(+:sum, result) schedule(static,1)
for (i = 0; i < num_threads; i++)
{
int this_result;
// Feed each part of the string to the stream reader:
this_result = base64_stream_decode(&state, src + i * len, len, out + i * len * 3 / 4, &s);
sum += s;
result += this_result;
}
}
// If `result' equals `-num_threads', then all threads returned -1,
// indicating that the requested codec is not available:
if (result == -num_threads) {
return -1;
}
// If `result' does not equal `num_threads', then at least one of the
// threads hit a decode error:
if (result != num_threads) {
return 0;
}
// So far so good, now decode whatever remains in the buffer. Reuse the
// initial state, since we are at a 4-byte boundary:
state = initial_state;
result = base64_stream_decode(&state, src + num_threads * len, last_len, out + num_threads * len * 3 / 4, &s);
sum += s;
*outlen = sum;
// If when decoding a whole block, we're still waiting for input then fail:
if (result && (state.bytes == 0)) {
return result;
}
return 0;
}
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