• test (15/15) Nov 07 2018 I am confused about the bitfields order.
• lithium iodate (20/35) Nov 07 2018 The bitfields start with the least significant bits:
• test (18/40) Nov 07 2018 After I use your code it working now.

test <test gmail.com> writes:

I am confused about the bitfields order.

mixin(bitfields!(
	bool, 	"fin",     	1,
	bool,   "rsv1", 	1,
	bool,   "rsv2", 	1,
	bool,   "rsv3", 	1,
	Opcode, "opcode", 	4,
		
	bool,   "mask", 	1,
	ubyte,  "_size", 	7,
));


output for first byte is 10000001 ,  the 2st byte 10000011

my code output:  opcode=8 mask=true size=65

the real size is 3 byte, and opcode is 1;

how to fix this ?

lithium iodate <whatdoiknow doesntexist.net> writes:

On Wednesday, 7 November 2018 at 13:05:49 UTC, test wrote:
 I am confused about the bitfields order.

 mixin(bitfields!(
 	bool, 	"fin",     	1,
 	bool,   "rsv1", 	1,
 	bool,   "rsv2", 	1,
 	bool,   "rsv3", 	1,
 	Opcode, "opcode", 	4,
 		
 	bool,   "mask", 	1,
 	ubyte,  "_size", 	7,
 ));


 output for first byte is 10000001 ,  the 2st byte 10000011

 my code output:  opcode=8 mask=true size=65

 the real size is 3 byte, and opcode is 1;

 how to fix this ?

The bitfields start with the least significant bits:
fin -> 1
rsv1 -> 0
rsv2 -> 0
rsv3 -> 0
opcode -> 1000 = 8

mask -> 1
_size -> 1000001 = 65

This order will likely be what you want:
mixin(bitfields!(
     opcode, "opcode", 4,
     bool,   "rsv3",   1,
     bool,   "rsv2",   1,
     bool,   "rsv1",   1,
     bool,   "fin",    1,

     ubyte,  "_size",  7,
     bool,   "mask",   1,
));

Also beware of endianness when mapping bytes to it.

test <test gmail.com> writes:

On Wednesday, 7 November 2018 at 14:22:43 UTC, lithium iodate 
wrote:
 On Wednesday, 7 November 2018 at 13:05:49 UTC, test wrote:
 I am confused about the bitfields order.

 The bitfields start with the least significant bits:
 fin -> 1
 rsv1 -> 0
 rsv2 -> 0
 rsv3 -> 0
 opcode -> 1000 = 8

 mask -> 1
 _size -> 1000001 = 65

 This order will likely be what you want:
 mixin(bitfields!(
     opcode, "opcode", 4,
     bool,   "rsv3",   1,
     bool,   "rsv2",   1,
     bool,   "rsv1",   1,
     bool,   "fin",    1,

     ubyte,  "_size",  7,
     bool,   "mask",   1,
 ));

 Also beware of endianness when mapping bytes to it.

After I use your code it working now.

my other question is: if the opcode bit cross byte, how do we 
define the bitfields ?

for example if the opcode is a 6 bit number instead 4bit :  
F1|R1|R1|R1|opcode6|Mask1|Size5

I has to split the opcode here ?

mixin(bitfields!(
      opcode, "opcode4", 4,
      bool,   "rsv3",   1,
      bool,   "rsv2",   1,
      bool,   "rsv1",   1,
      bool,   "fin",    1,

      ubyte,  "_size",  5,
      bool,   "mask",   1,
      bool,   "opcode2",   1,
  ));