jpeg: Optimise by replacing division with shifts.

diff --git a/grub-core/video/readers/jpeg.c b/grub-core/video/readers/jpeg.c
index 38ea2395a214cd9057bb303f91b46fc0facb4cca..c3e0df240d92525d37e0895925367e8488f6494e 100644 (file)
--- a/grub-core/video/readers/jpeg.c
+++ b/grub-core/video/readers/jpeg.c
@@ -94,7 +94,7 @@ struct grub_jpeg_data
   jpeg_data_unit_t crdu;
   jpeg_data_unit_t cbdu;
 
-  unsigned vs, hs;
+  unsigned log_vs, log_hs;
   int dri;
   unsigned r1;
 
@@ -315,11 +315,14 @@ grub_jpeg_decode_sof (struct grub_jpeg_data *data)
       ss = grub_jpeg_get_byte (data);  /* Sampling factor.  */
       if (!id)
        {
-         data->vs = ss & 0xF;  /* Vertical sampling.  */
-         data->hs = ss >> 4;   /* Horizontal sampling.  */
-         if ((data->vs > 2) || (data->hs > 2) || (data->vs == 0) || (data->hs == 0))
+         grub_uint8_t vs, hs;
+         vs = ss & 0xF;        /* Vertical sampling.  */
+         hs = ss >> 4; /* Horizontal sampling.  */
+         if ((vs > 2) || (hs > 2) || (vs == 0) || (hs == 0))
            return grub_error (GRUB_ERR_BAD_FILE_TYPE,
                               "jpeg: sampling method not supported");
+         data->log_vs = (vs == 2);
+         data->log_hs = (hs == 2);
        }
       else if (ss != JPEG_SAMPLING_1x1)
        return grub_error (GRUB_ERR_BAD_FILE_TYPE,
@@ -616,10 +619,10 @@ grub_jpeg_decode_data (struct grub_jpeg_data *data)
   unsigned c1, vb, hb, nr1, nc1;
   int rst = data->dri;
 
-  vb = data->vs * 8;
-  hb = data->hs * 8;
-  nr1 = (data->image_height + vb - 1) / vb;
-  nc1 = (data->image_width + hb - 1) / hb;
+  vb = 8 << data->log_vs;
+  hb = 8 << data->log_hs;
+  nr1 = (data->image_height + vb - 1) >> (3 + data->log_vs);
+  nc1 = (data->image_width + hb - 1)  >> (3 + data->log_hs);
 
   for (; data->r1 < nr1 && (!data->dri || rst);
        data->r1++, data->bitmap_ptr += (vb * data->image_width - hb * nc1) * 3)
@@ -629,8 +632,8 @@ grub_jpeg_decode_data (struct grub_jpeg_data *data)
        unsigned r2, c2, nr2, nc2;
        grub_uint8_t *ptr2;
 
-       for (r2 = 0; r2 < data->vs; r2++)
-         for (c2 = 0; c2 < data->hs; c2++)
+       for (r2 = 0; r2 < (1U << data->log_vs); r2++)
+         for (c2 = 0; c2 < (1U << data->log_hs); c2++)
            grub_jpeg_decode_du (data, 0, data->ydu[r2 * 2 + c2]);
 
        if (data->color_components >= 3)
@@ -652,7 +655,7 @@ grub_jpeg_decode_data (struct grub_jpeg_data *data)
              unsigned i0;
              int yy;
 
-             i0 = (r2 / data->vs) * 8 + (c2 / data->hs);
+             i0 = (r2 >> data->log_vs) * 8 + (c2 >> data->log_hs);
              yy = data->ydu[(r2 / 8) * 2 + (c2 / 8)][(r2 % 8) * 8 + (c2 % 8)];
 
              if (data->color_components >= 3)