+ # combined with vec_el_counts {0:1, 1:1, 2:2, 3:4} we have:
+ # elwidth=0b00 1x 24-bit
+ # elwidth=0b01 1x 12-bit
+ # elwidth=0b10 2x 5-bit
+ # elwidth=0b11 4x 6-bit
+ #
+ # bmask<--------1<----0<---------10<---0<-------1<0<----0<---0<----00<---0
+ # always unused:| | | || | | | | | | || |
+ # 1111111111000000 1111111111000000 1111111100000000 0000000000000000
+ # | | | || | | | | | | || |
+ # 0b00 xxxxxxxxxxxxxxxx xxxxxxxxxxxxxxxx xxxxxxxx........ ..............24|
+ # 0b01 xxxxxxxxxxxxxxxx xxxxxxxxxxxxxxxx xxxxxxxxxxxxxxxx xxxx..........12|
+ # 0b10 xxxxxxxxxxxxxxxx xxxxxxxxxxx....5|xxxxxxxxxxxxxxxx xxxxxxxxxxx....5|
+ # 0b11 xxxxxxxxxx.....6|xxxxxxxxxx.....6|xxxxxxxxxx.....6|xxxxxxxxxx.....6|
+ # ^ ^ ^^ ^ ^ ^ ^ ^ ^^
+ # ppoints: | | || | | | | | ||
+ # | bit-48 /\ | bit-24-/ | | bit-12 /\-bit-5
+ # bit-54 bit-38-/ \ bit-32 | bit-16 /
+ # bit-37 bit-22 bit-6
+