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Dear Everyone:

The# _mm_shuffle_epi8, on msdn I do not know it means.

rn = (maskn & 0x80) ? 0 : SELECT(a, maskn & 0x0f)

SELECT(a, n) extracts the nth 8-bit parameter from a. The 0th 8-bit parameter is the least significant 8-bits.

I do not know what is the the SELECT(a, n)

the msdn exmaple, :

Gaiger_Chen

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04-06-2011
04:03 AM

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The

rn = (maskn & 0x80) ? 0 : SELECT(a, maskn & 0x0f)

SELECT(a, n) extracts the nth 8-bit parameter from a. The 0th 8-bit parameter is the least significant 8-bits.

I do not know what is the the SELECT(a, n)

the msdn exmaple, :

a.m128i_i8[15] = -1; ---> 1111 1111mask.m128i_u8[15] = 0x00; -> get 0th 8-bit

I do not know why the output is 1 ( 0000 0001).

similiar fora.m128i_i8[13] = -64; ---> 1100 0000mask.m128i_u8[13] = 0x02; ->get 2th bit

why the output is 4 ? (0000 0100) ??

thank you lots.

Accepted Solutions

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Dear all:

I have regonize the SELECT(a, n).

is is the the ith**byte**, but bit.

for example:

so the

Gaiger_Chen

New Contributor I

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04-06-2011
08:12 AM

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I have regonize the SELECT(a, n).

is is the the ith

for example:

so the

mask.m128i_u8[1] = 0x0E; -> select Eth (14th) byte, it isa.m128i_i8[14] = -128;mask.m128i_u8[11] = 0x04; -> select the 4th byte, it isa.m128i_i8[4] = 16.

1 Reply

Highlighted
Dear all:

I have regonize the SELECT(a, n).

is is the the ith**byte**, but bit.

for example:

so the

Gaiger_Chen

New Contributor I

- Mark as New
- Bookmark
- Subscribe
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04-06-2011
08:12 AM

76 Views

I have regonize the SELECT(a, n).

is is the the ith

for example:

so the

mask.m128i_u8[1] = 0x0E; -> select Eth (14th) byte, it isa.m128i_i8[14] = -128;mask.m128i_u8[11] = 0x04; -> select the 4th byte, it isa.m128i_i8[4] = 16.

For more complete information about compiler optimizations, see our Optimization Notice.