simple_v_extension/shape_table_format.mdwn

   1 Shape is 32-bits.  When SHAPE is set entirely to zeros, remapping is
   2 disabled: the register's elements are a linear (1D) vector.
   3
   4 | 31..30   | 29..24 | 23..21  | 20..18  | 17..12  | 11..6   | 5..0    |
   5 | -------- | ------ | ------- | ------- | ------- | -------- | ------- |
   6 | applydim | offset | invxyz  | permute | zdimsz  | ydimsz  | xdimsz  |
   7
   8 applydim will set to zero the dimensions less than this. applydim=0
   9 applies all three. applydim=1 applies y and z. applydim=2 applys only
  10 z. applydim=3 is reserved.
  11
  12 invxyz will invert the start index of each of x, y or z. If invxyz[0] is
  13 zero then x-dimensional counting begins from 0 and increments, otherwise
  14 it begins from xdimsz-1 and iterates down to zero. Likewise for y and z.
  15
  16 offset will have the effect equivalent to the sequential element loop
  17 to appear to run for offset (additional) iterations prior to actually
  18 generating output.
  19
  20 xdimsz, ydimsz and zdimsz are offset by 1, such that a value of 0 indicates
  21 that the array dimensionality for that dimension is 1.  A value of xdimsz=2
  22 would indicate that in the first dimension there are 3 elements in the
  23 array.  The format of the array is therefore as follows:
  24
  25     array[xdim+1][ydim+1][zdim+1]
  26
  27 However whilst illustrative of the dimensionality, that does not take the
  28 "permute" setting into account.  "permute" may be any one of six values
  29 (0-5, with values of 6 and 7 being reserved, and not legal).  The table
  30 below shows how the permutation dimensionality order works:
  31
  32 | permute | order | array format             |
  33 | ------- | ----- | ------------------------ |
  34 | 000     | 0,1,2 | (xdim+1)(ydim+1)(zdim+1) |
  35 | 001     | 0,2,1 | (xdim+1)(zdim+1)(ydim+1) |
  36 | 010     | 1,0,2 | (ydim+1)(xdim+1)(zdim+1) |
  37 | 011     | 1,2,0 | (ydim+1)(zdim+1)(xdim+1) |
  38 | 100     | 2,0,1 | (zdim+1)(xdim+1)(ydim+1) |
  39 | 101     | 2,1,0 | (zdim+1)(ydim+1)(xdim+1) |
  40
  41 In other words, the "permute" option changes the order in which
  42 nested for-loops over the array would be done.
  43