openpower/sv/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..28 | 27..24 | 23..21 | 20..18  | 17..12  | 11..6   | 5..0    |
   5 | ------ | ------ | ------ | ------ | ------- | ------- | ------- | ------- |
   6 | 0b00   | skip   | offset | invxyz | permute | zdimsz  | ydimsz  | xdimsz  |
   7 | 0b01   | submode| offset | invxyz | rsvd    | rsvd    | rsvd    | xdimsz  |
   8
   9 mode sets different behaviours (straight matrix multiply, FFT, DCT).
  10
  11 * **mode=0b00** sets straight Matrix Mode
  12 * **mode=0b01** sets "FFT / DCT" mode and activates submodes
  13
  14 submode further selects schedules for FFT and DCT.
  15
  16 * **submode=0b000** selects the ``j`` offset of the innermost for-loop
  17   of Tukey-Cooley
  18 * **submode=0b010** selects the ``j+halfsize`` offset of the innermost for-loop
  19   of Tukey-Cooley
  20 * **submode=0b011** selects the ``k`` of exptable (which coefficient)
  21
  22 skip allows dimensions to be skipped from being included in the resultant
  23 output index.  this allows sequences to be repeated: ```0 0 0 1 1 1 2 2 2 ...``` or in the case of skip=0b11 this results in modulo ```0 1 2 0 1 2 ...```
  24
  25 * **skip=0b00** indicates no dimensions to be skipped
  26 * **skip=0b01** sets "skip 1st dimension"
  27 * **skip=0b10** sets "skip 2nd dimension"
  28 * **skip=0b11** sets "skip 3rd dimension"
  29
  30 invxyz will invert the start index of each of x, y or z. If invxyz[0] is
  31 zero then x-dimensional counting begins from 0 and increments, otherwise
  32 it begins from xdimsz-1 and iterates down to zero. Likewise for y and z.
  33
  34 offset will have the effect of offsetting the result by ```offset``` elements:
  35
  36     for i in 0..VL-1:
  37         GPR(RT + remap(i) + SVSHAPE.offset) = ....
  38
  39 this appears redundant because the register RT could simply be changed by a compiler, until element width overrides are introduced.  also
  40 bear in mind that unlike a static compiler SVSHAPE.offset may
  41 be set dynamically at runtime.
  42
  43 xdimsz, ydimsz and zdimsz are offset by 1, such that a value of 0 indicates
  44 that the array dimensionality for that dimension is 1. any dimension
  45 not intended to be used must have its value set to 0 (dimensionality
  46 of 1).  A value of xdimsz=2 would indicate that in the first dimension
  47 there are 3 elements in the array.  For example, to create a 2D array
  48 X,Y of dimensionality X=3 and Y=2, set xdimsz=2, ydimsz=1 and zdimsz=0
  49
  50 The format of the array is therefore as follows:
  51
  52     array[xdimsz+1][ydimsz+1][zdimsz+1]
  53
  54 However whilst illustrative of the dimensionality, that does not take the
  55 "permute" setting into account.  "permute" may be any one of six values
  56 (0-5, with values of 6 and 7 being reserved, and not legal).  The table
  57 below shows how the permutation dimensionality order works:
  58
  59 | permute | order | array format             |
  60 | ------- | ----- | ------------------------ |
  61 | 000     | 0,1,2 | (xdim+1)(ydim+1)(zdim+1) |
  62 | 001     | 0,2,1 | (xdim+1)(zdim+1)(ydim+1) |
  63 | 010     | 1,0,2 | (ydim+1)(xdim+1)(zdim+1) |
  64 | 011     | 1,2,0 | (ydim+1)(zdim+1)(xdim+1) |
  65 | 100     | 2,0,1 | (zdim+1)(xdim+1)(ydim+1) |
  66 | 101     | 2,1,0 | (zdim+1)(ydim+1)(xdim+1) |
  67
  68 In other words, the "permute" option changes the order in which
  69 nested for-loops over the array would be done.  See executable
  70 python reference code for further details.
  71