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Example 6-6 Third set of code replacements
Original code:
ix = (tmp - MIN) & 0xFFF;
jx
= (ix + 1) & 0xFFF;
x_ix = x - (float)tmp;
x_jx = x_ix - 1.0;
sx = x_ix * x_ix * (3.0 - 2.0 * x_ix));
tx = 1.0 - sx;
New vectorized code:
iaux = vec_sub( tmp, imin );
ix
= vec_and( iaux, iFFF );
jx = vec_and( vec_add( ix, ione ), iFFF );
faux = vec_ctf( tmp, 0 );
x_ix = vec_sub( x, faux );
x_jx = vec_sub( x_ix, fone );
sx = vec_madd( fmtwo, x_ix, fthree );
faux = vec_madd( x_ix, x_ix, fzero );
sx = vec_madd( sx, faux, fzero );
tx = vec_sub( fone, sx );
Now that we have finished with the work related to component x, we should do the same work
for components y and z.
Up to now it has been relatively straight forward conversion. With a small set of data, just
three vectors, we have produced a lot of vector instructions, thus speeding up our application.
However, the next set of instructions will be much more difficult to vectorize.
As shown in Example 6-7, the original code uses ix, jx, iy, and jy to index an integer array.
So, can we do that with vectors? The correct answer is no. However, we still can do it with
multiple scalar operations. Now, it is time to start making use of those structures that we
presented in previous section. Those structures allow us to access the different elements of
the vector.
Example 6-7 Fourth set of code replacements
Original code:
ixiy_hash = hashTable[hashTable[ix]^iy];
jxiy_hash = hashTable[hashTable[jx]^iy];
ixjy_hash = hashTable[hashTable[ix]^jy];
jxjy_hash = hashTable[hashTable[jx]^jy];
New vectorized
ixiy_hash.e[0]
ixiy_hash.e[1]
ixiy_hash.e[2]
ixiy_hash.e[3]
code:
= hashTable[hashTable[ix.e[0]]^iy.e[0]];
= hashTable[hashTable[ix.e[1]]^iy.e[1]];
= hashTable[hashTable[ix.e[2]]^iy.e[2]];
= hashTable[hashTable[ix.e[3]]^iy.e[3]];
jxiy_hash.e[0]
jxiy_hash.e[1]
jxiy_hash.e[2]
jxiy_hash.e[3]
=
=
=
=
hashTable[hashTable[jx.e[0]]^iy.e[0]];
hashTable[hashTable[jx.e[1]]^iy.e[1]];
hashTable[hashTable[jx.e[2]]^iy.e[2]];
hashTable[hashTable[jx.e[3]]^iy.e[3]];
ixjy_hash.e[0]
ixjy_hash.e[1]
ixjy_hash.e[2]
ixjy_hash.e[3]
=
=
=
=
hashTable[hashTable[ix.e[0]]^jy.e[0]];
hashTable[hashTable[ix.e[1]]^jy.e[1]];
hashTable[hashTable[ix.e[2]]^jy.e[2]];
hashTable[hashTable[ix.e[3]]^jy.e[3]];
Chapter 6. A case study
105