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Unroll the 3x3 convolution case

Gets us about 2x speedup on x86

--- a/dnn/nnet.c

+++ b/dnn/nnet.c

@@ -394,6 +394,34 @@

    }

 }

+void conv2d_3x3_float(float *out, const float *weights, int in_channels, int out_channels, const float *in, int height, int hstride)

+{

+   int i;

+   int in_stride;

+   int kheight, ktime;

+   kheight = ktime = 3;

+   in_stride = height+kheight-1;

+   for (i=0;i<out_channels;i++) {

+      int m;

+      OPUS_CLEAR(&out[i*hstride], height);

+      for (m=0;m<in_channels;m++) {

+         int j;

+         for (j=0;j<height;j++) {

+            /* Unrolled version of previous function -- compiler will figure out the indexing simplifications. */

+            out[i*hstride + j] += weights[i*in_channels*ktime*kheight + m*ktime*kheight + 0*kheight + 0]*in[0*in_channels*in_stride + m*in_stride + j + 0]

+                                + weights[i*in_channels*ktime*kheight + m*ktime*kheight + 0*kheight + 1]*in[0*in_channels*in_stride + m*in_stride + j + 1]

+                                + weights[i*in_channels*ktime*kheight + m*ktime*kheight + 0*kheight + 2]*in[0*in_channels*in_stride + m*in_stride + j + 2]

+                                + weights[i*in_channels*ktime*kheight + m*ktime*kheight + 1*kheight + 0]*in[1*in_channels*in_stride + m*in_stride + j + 0]

+                                + weights[i*in_channels*ktime*kheight + m*ktime*kheight + 1*kheight + 1]*in[1*in_channels*in_stride + m*in_stride + j + 1]

+                                + weights[i*in_channels*ktime*kheight + m*ktime*kheight + 1*kheight + 2]*in[1*in_channels*in_stride + m*in_stride + j + 2]

+                                + weights[i*in_channels*ktime*kheight + m*ktime*kheight + 2*kheight + 0]*in[2*in_channels*in_stride + m*in_stride + j + 0]

+                                + weights[i*in_channels*ktime*kheight + m*ktime*kheight + 2*kheight + 1]*in[2*in_channels*in_stride + m*in_stride + j + 1]

+                                + weights[i*in_channels*ktime*kheight + m*ktime*kheight + 2*kheight + 2]*in[2*in_channels*in_stride + m*in_stride + j + 2];

+               }

+      }

+   }

+}

+

 #define MAX_CONV2D_INPUTS 8192

 void compute_conv2d(const Conv2dLayer *conv, float *out, float *mem, const float *in, int height, int hstride, int activation)

@@ -409,7 +437,10 @@

    OPUS_COPY(&in_buf[(conv->ktime-1)*time_stride], in, time_stride);

    OPUS_COPY(mem, &in_buf[time_stride], (conv->ktime-1)*time_stride);

    bias = conv->bias;

-   conv2d_float(out, conv->float_weights, conv->in_channels, conv->out_channels, conv->ktime, conv->kheight, in_buf, height, hstride);

+   if (conv->kheight == 3 && conv->ktime == 3)

+     conv2d_3x3_float(out, conv->float_weights, conv->in_channels, conv->out_channels, in_buf, height, hstride);

+   else

+     conv2d_float(out, conv->float_weights, conv->in_channels, conv->out_channels, conv->ktime, conv->kheight, in_buf, height, hstride);

    if (bias != NULL) {

      for (i=0;i<conv->out_channels;i++) {

        int j;

-- 

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