How to get the C-compiler to use RLC and ACC.x

I don't think that it is quite what you are looking for, but there are a number of intrinsic functions provided by Keil and detailed in the C51 Compiler Manual. Most of these intrinsic functions roll a 1, 2 or 4-byte variable n places left or right. Although not perfect, the code for 1 and 2 byte variables is put in-line (rather than a function call) and they make use of RLC type instructions so that they are reasonably fast when shifting by a small number of bits.

In spite of the claims of the manual, the rolls for 4-byte variables are actually implemented by library calls. Also, if I recall correctly from the last time that I looked, the compiler always codes a loop even when the roll is know to be just one bit.

For a faster way to roll long variables, see: http://www.keil.com/forum/docs/thread1252.asp

C can access any bit of a variable by various means. See http://www.keil.com/forum/docs/thread554.asp for some examples The most portable method it to use masks, but I don't think that that will generate an ACC.x type reference. The most obvious method is to use a structure containing fields with a width of just one bit, this will cause ACC.x type instructions to be generated, but Keil does not seem to make very efficient use of them (see http://www.keil.com/forum/docs/thread1291.asp ).

In the end, if there are just a few very specific functions that you want to perform then your best bet is going to be to write an assembly language sub-routine that you can call from a C function.

I don't think that it is quite what you are looking for, but there are a number of intrinsic functions provided by Keil and detailed in the C51 Compiler Manual. Most of these intrinsic functions roll a 1, 2 or 4-byte variable n places left or right. Although not perfect, the code for 1 and 2 byte variables is put in-line (rather than a function call) and they make use of RLC type instructions so that they are reasonably fast when shifting by a small number of bits.

In spite of the claims of the manual, the rolls for 4-byte variables are actually implemented by library calls. Also, if I recall correctly from the last time that I looked, the compiler always codes a loop even when the roll is know to be just one bit.

For a faster way to roll long variables, see: http://www.keil.com/forum/docs/thread1252.asp

C can access any bit of a variable by various means. See http://www.keil.com/forum/docs/thread554.asp for some examples The most portable method it to use masks, but I don't think that that will generate an ACC.x type reference. The most obvious method is to use a structure containing fields with a width of just one bit, this will cause ACC.x type instructions to be generated, but Keil does not seem to make very efficient use of them (see http://www.keil.com/forum/docs/thread1291.asp ).

In the end, if there are just a few very specific functions that you want to perform then your best bet is going to be to write an assembly language sub-routine that you can call from a C function.