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Option use of SSE intrinsics (still trying to convince gcc not to move the
input data across all registers)

--- a/libcelt/vq.c

+++ b/libcelt/vq.c

@@ -34,6 +34,25 @@

 #include "cwrs.h"

 #include "vq.h"

+/* Enable this or define your own implementation if you want to speed up the

+   VQ search (used in inner loop only) */

+#if 0

+#include <xmmintrin.h>

+static inline float approx_sqrt(float x)

+{

+   _mm_store_ss(&x, _mm_sqrt_ss(_mm_set_ss(x)));

+   return x;

+}

+static inline float approx_inv(float x)

+{

+   _mm_store_ss(&x, _mm_rcp_ss(_mm_set_ss(x)));

+   return x;

+}

+#else

+#define approx_sqrt(x) (sqrt(x))

+#define approx_inv(x) (1.f/(x))

+#endif

+

 struct NBest {

    float score;

    float gain;

@@ -115,7 +134,7 @@

       }

       for (m=0;m<Lupdate;m++)

-         nbest[m]->score = -1e10;

+         nbest[m]->score = -1e10f;

       for (m=0;m<L2;m++)

       {

@@ -136,14 +155,14 @@

                /* Updating the sums of the new pulse(s) */

                tmp_xy = xy[m] + s*x[j]               - alpha*s*p[j]*Rxp;

-               tmp_yy = yy[m] + 2*s*y[m][j] + s*s      +s*s*alpha*alpha*p[j]*p[j]*Rpp - 2*alpha*s*p[j]*yp[m] - 2*s*s*alpha*p[j]*p[j];

-               tmp_yp = yp[m] + s*p[j]               *(1-alpha*Rpp);

+               tmp_yy = yy[m] + 2.f*s*y[m][j] + s*s      +s*s*alpha*alpha*p[j]*p[j]*Rpp - 2.f*alpha*s*p[j]*yp[m] - 2.f*s*s*alpha*p[j]*p[j];

+               tmp_yp = yp[m] + s*p[j]               *(1.f-alpha*Rpp);

                /* Compute the gain such that ||p + g*y|| = 1 */

-               g = (sqrt(tmp_yp*tmp_yp + tmp_yy - tmp_yy*Rpp) - tmp_yp)/tmp_yy;

+               g = (approx_sqrt(tmp_yp*tmp_yp + tmp_yy - tmp_yy*Rpp) - tmp_yp)*approx_inv(tmp_yy);

                /* Knowing that gain, what the error: (x-g*y)^2 

                   (result is negated and we discard x^2 because it's constant) */

-               score = 2*g*tmp_xy - g*g*tmp_yy;

+               score = 2.f*g*tmp_xy - g*g*tmp_yy;

                if (score>nbest[Lupdate-1]->score)

                {