Shape is 32-bits. When SHAPE is set entirely to zeros, remapping is
disabled: the register's elements are a linear (1D) vector.
-| 31..30 | 29..28 | 27..24 | 23..21 | 20..18 | 17..12 | 11..6 | 5..0 |
-| ------ | ------ | ------ | ------ | ------- | ------- | ------- | ------- |
-| 0b00 | skip | offset | invxyz | permute | zdimsz | ydimsz | xdimsz |
-| 0b01 | submode| offset | invxyz | submode2| rsvd | rsvd | xdimsz |
-| 0b00 | elwidth| offset |skip/invxy|0b110/0b111|SVGPR| ydimsz | xdimsz |
+|31.30|29..28 |27..24| 23..21 | 20..18 | 17..12 |11..6 |5..0 | Mode |
+|---- |------ |------| ------ | ------- | ------- |----- |----- | ----- |
+|0b00 |skip |offset| invxyz | permute | zdimsz |ydimsz|xdimsz|Matrix |
+|0b00 |elwidth|offset|skip/invxy|0b110/0b111|SVGPR|ydimsz|xdimsz|Indexed|
+|0b01 |submode|offset| invxyz | submode2| rsvd |rsvd |xdimsz|DCT/FFT|
mode sets different behaviours (straight matrix multiply, FFT, DCT).