How about these...?
http://software.intel.com/sites/products/documentation/hpc/composerxe/en-us/cpp/mac/intref_cls/common/intref_bk_convertpost32_hf.htm
On Wed, Jul 20, 2011 at 4:59 PM, James Bowman jamesb-...@excamera.com wrote:
Here's my conversion code. It handles infinity, overflows and underflows.
But it does not handle denormals or NaNs. It also truncates the mantissa,
instead of rounding it. As I clock it, it's about 2X the speed of the
conversion in Half.
#include xmmintrin.h
#define Ki(x) _mm_set_epi32((x),(x),(x),(x))
// Convert n floats at src to half-floats at dst. n is a multiple of 4
static void qhalf(unsigned short *dst, const float *src, size_t n)
{
while (n) {
__m128i full = _mm_loadu_si128((__m128i*)src);
__m128i sign = full Ki(1UL 31); // extract
sign
__m128i mantissa = full Ki((1 23) - 1); // extract
mantissa
__m128i exp8 = _mm_srli_epi32(full, 23) Ki(0xff); // extract
exponent
__m128i is_huge = _mm_cmpgt_epi32(exp8, Ki(0x8f)); // means flush
to INF
__m128i is_tiny = _mm_cmplt_epi32(exp8, Ki(0x70)); // means flush
to zero
__m128i exp5 = _mm_add_epi32(exp8, Ki(-0x7f + 0xf)); // rebias
exponent
// INF is represented by exponent=0x1f and mantissa=0
exp5 = _mm_and_si128(_mm_or_si128(exp5, is_huge), Ki(0x1f));
mantissa = _mm_andnot_si128(is_huge, mantissa);
__m128i half = _mm_slli_epi32(exp5, 10) | _mm_srli_epi32(mantissa, 13);
// Underflow: force to zero
half = _mm_andnot_si128(is_tiny, half);
// apply sign
half = _mm_or_si128(half, _mm_srai_epi32(sign, 16));
_mm_storel_pi((__m64*)dst, (__m128)_mm_packs_epi32((__m128i)half,
(__m128i)half));
dst += 4;
src += 4;
n -= 4;
}
}
On Tue, Jul 19, 2011 at 11:19 AM, Florian Kainz ka...@ilm.com wrote:
Have any of you tried to convert vectors of 32-bit floating-point
numbers to vectors of 16-bit floating-point numbers in a way that
is faster than calling OpenEXR's half-from-float constructor for
each vector element? Maybe using MMX, SSE or AVX instructions?
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--
James Bowman
http://www.excamera.com/sphinx/articles-openexr.html
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