}
-static unsigned long SelectHostBufferSize( unsigned long suggestedLatencyFrames, unsigned long userFramesPerBuffer,
- PaAsioDriverInfo *driverInfo )
+/* return the next power of two >= x.
+ Returns the input parameter if it is already a power of two.
+ http://stackoverflow.com/questions/364985/algorithm-for-finding-the-smallest-power-of-two-thats-greater-or-equal-to-a-giv
+*/
+static unsigned long NextPowerOfTwo( unsigned long x )
+{
+ --x;
+ x |= x >> 1;
+ x |= x >> 2;
+ x |= x >> 4;
+ x |= x >> 8;
+ x |= x >> 16;
+ /* If you needed to deal with numbers > 2^32 the following would be needed.
+ For latencies, we don't deal with values this large.
+ x |= x >> 16;
+ */
+
+ return x + 1;
+}
+
+
+static unsigned long SelectHostBufferSizeForUnspecifiedUserFramesPerBuffer(
+ unsigned long suggestedLatencyFrames, PaAsioDriverInfo *driverInfo )
{
- unsigned long result;
+ /* Choose a host buffer size based only on suggestedLatencyFrames and the
+ device's supported buffer sizes. Always returns a valid value.
+ */
- if( suggestedLatencyFrames == 0 )
+ unsigned long result;
+
+ if( suggestedLatencyFrames <= (unsigned long)driverInfo->bufferMinSize )
{
- result = driverInfo->bufferPreferredSize;
+ result = driverInfo->bufferMinSize;
}
- else{
- if( suggestedLatencyFrames <= (unsigned long)driverInfo->bufferMinSize )
+ else if( suggestedLatencyFrames >= (unsigned long)driverInfo->bufferMaxSize )
+ {
+ result = driverInfo->bufferMaxSize;
+ }
+ else
+ {
+ if( driverInfo->bufferGranularity == 0 ) /* single fixed host buffer size */
{
- result = driverInfo->bufferMinSize;
+ /* The documentation states that bufferGranularity should be zero
+ when bufferMinSize, bufferMaxSize and bufferPreferredSize are the
+ same. We assume that is the case.
+ */
+
+ result = driverInfo->bufferPreferredSize;
}
- else if( suggestedLatencyFrames >= (unsigned long)driverInfo->bufferMaxSize )
+ else if( driverInfo->bufferGranularity == -1 ) /* power-of-two */
{
- result = driverInfo->bufferMaxSize;
+ /* We assume bufferMinSize and bufferMaxSize are powers of two. */
+
+ result = NextPowerOfTwo( suggestedLatencyFrames );
+
+ if( result < (unsigned long)driverInfo->bufferMinSize )
+ result = driverInfo->bufferMinSize;
+
+ if( result > (unsigned long)driverInfo->bufferMaxSize )
+ result = driverInfo->bufferMaxSize;
}
- else
+ else /* modulo bufferGranularity */
{
- if( driverInfo->bufferGranularity == -1 )
- {
- /* power-of-two */
- result = 2;
+ /* round up to the next multiple of granularity */
+ unsigned long n = (suggestedLatencyFrames + driverInfo->bufferGranularity - 1)
+ / driverInfo->bufferGranularity;
+
+ result = n * driverInfo->bufferGranularity;
- while( result < suggestedLatencyFrames )
- result *= 2;
+ if( result < (unsigned long)driverInfo->bufferMinSize )
+ result = driverInfo->bufferMinSize;
- if( result < (unsigned long)driverInfo->bufferMinSize )
- result = driverInfo->bufferMinSize;
+ if( result > (unsigned long)driverInfo->bufferMaxSize )
+ result = driverInfo->bufferMaxSize;
+ }
+ }
- if( result > (unsigned long)driverInfo->bufferMaxSize )
- result = driverInfo->bufferMaxSize;
- }
- else if( driverInfo->bufferGranularity == 0 )
- {
- /* the documentation states that bufferGranularity should be
- zero when bufferMinSize, bufferMaxSize and
- bufferPreferredSize are the same. We assume that is the case.
- */
+ return result;
+}
- result = driverInfo->bufferPreferredSize;
- }
- else
- {
- /* modulo granularity */
- unsigned long remainder =
- suggestedLatencyFrames % driverInfo->bufferGranularity;
+static unsigned long SelectHostBufferSizeForSpecifiedUserFramesPerBuffer(
+ unsigned long suggestedLatencyFrames, unsigned long userFramesPerBuffer,
+ PaAsioDriverInfo *driverInfo )
+{
+ /* Select a host buffer size conforming to suggestedLatencyFrames
+ and the device's supported buffer sizes.
+ The return value will always be a multiple of userFramesPerBuffer.
+ If a valid buffer size can not be found the function returns 0.
+
+ The current implementation uses a simple iterative search for clarity.
+ Feel free to suggest a closed form solution.
+ */
+ unsigned long result = 0;
+
+ assert( userFramesPerBuffer != 0 );
+
+ if( driverInfo->bufferGranularity == 0 ) /* single fixed host buffer size */
+ {
+ /* The documentation states that bufferGranularity should be zero
+ when bufferMinSize, bufferMaxSize and bufferPreferredSize are the
+ same. We assume that is the case.
+ */
- if( remainder == 0 )
- {
- result = suggestedLatencyFrames;
- }
- else
- {
- result = suggestedLatencyFrames
- + (driverInfo->bufferGranularity - remainder);
+ if( (driverInfo->bufferPreferredSize % userFramesPerBuffer) == 0 )
+ result = driverInfo->bufferPreferredSize;
+ }
+ else if( driverInfo->bufferGranularity == -1 ) /* power-of-two */
+ {
+ /* We assume bufferMinSize and bufferMaxSize are powers of two. */
- if( result > (unsigned long)driverInfo->bufferMaxSize )
- result = driverInfo->bufferMaxSize;
- }
- }
- }
+ /* Search all powers of two in the range [bufferMinSize,bufferMaxSize]
+ for multiples of userFramesPerBuffer. We prefer the first multiple
+ that is equal or greater than suggestedLatencyFrames, or failing
+ that, the largest multiple less than suggestedLatencyFrames.
+ */
+ unsigned long x = (unsigned long)driverInfo->bufferMinSize;
+ do {
+ if( (x % userFramesPerBuffer) == 0 )
+ {
+ /* any power-of-two multiple of userFramesPerBuffer is acceptable */
+ result = x;
+ if( result >= suggestedLatencyFrames )
+ break; /* stop. a value >= to suggestedLatencyFrames is ideal. */
+ }
+
+ x *= 2;
+ } while( x <= (unsigned long)driverInfo->bufferMaxSize );
}
+ else /* modulo granularity */
+ {
+ /* We assume bufferMinSize is a multiple of bufferGranularity. */
- return result;
+ /* Search all multiples of bufferGranularity in the range
+ [bufferMinSize,bufferMaxSize] for multiples of userFramesPerBuffer.
+ We prefer the first multiple that is equal or greater than
+ suggestedLatencyFrames, or failing that, the largest multiple less
+ than suggestedLatencyFrames.
+ */
+ unsigned long x = (unsigned long)driverInfo->bufferMinSize;
+ do {
+ if( (x % userFramesPerBuffer) == 0 )
+ {
+ /* any power-of-two multiple of userFramesPerBuffer is acceptable */
+ result = x;
+ if( result >= suggestedLatencyFrames )
+ break; /* stop. a value >= to suggestedLatencyFrames is ideal. */
+ }
+
+ x += driverInfo->bufferGranularity;
+ } while( x <= (unsigned long)driverInfo->bufferMaxSize );
+ }
+
+ return result;
+}
+
+
+static unsigned long SelectHostBufferSize( unsigned long suggestedLatencyFrames,
+ unsigned long userFramesPerBuffer, PaAsioDriverInfo *driverInfo )
+{
+ unsigned long result = 0;
+
+ /* We select a host buffer size based on the following requirements
+ (in priority order):
+
+ 1. The host buffer size must be permissible according to the ASIO
+ driverInfo buffer size constraints (min, max, granularity or
+ powers-of-two).
+
+ 2. If the user specifies a non-zero framesPerBuffer parameter
+ (userFramesPerBuffer here) the host buffer should be a multiple of
+ this (subject to the constraints in (1) above).
+
+ [NOTE: Where no permissible host buffer size is a multiple of
+ userFramesPerBuffer, we choose a value as if userFramesPerBuffer were
+ zero (i.e. we ignore it). This strategy is open for review ~ perhaps
+ there are still "more optimal" buffer sizes related to
+ userFramesPerBuffer that we could use.]
+
+ 3. The host buffer size should be greater than or equal to
+ suggestedLatencyFrames, subject to (1) and (2) above. Where it is not
+ possible to select a host buffer size equal or greater than
+ suggestedLatencyFrames, the highest buffer size conforming to (1)
+ and (2) should be chosen.
+ */
+
+ if( userFramesPerBuffer != 0 )
+ {
+ /* userFramesPerBuffer is specified, try to find a buffer size that's a multiple of it */
+ result = SelectHostBufferSizeForSpecifiedUserFramesPerBuffer(
+ suggestedLatencyFrames, userFramesPerBuffer, driverInfo );
+ }
+
+ if( result == 0 )
+ {
+ /* either userFramesPerBuffer was not specified, or we couldn't find a host buffer size that
+ is a multiple of it. Select a host buffer size according to suggestedLatencyFrames
+ and the ASIO driverInfo buffer size constraints.
+ */
+ result = SelectHostBufferSizeForUnspecifiedUserFramesPerBuffer(
+ suggestedLatencyFrames, driverInfo );
+ }
+
+ return result;
}
projects / portaudio / commitdiff