ARC GNU support for DSP instructions

Intro

ARCHS and ARCEM processors are adding support for fixed-point operations via DSP instructions. These instructions are also used/supported by the ARC GNU compiler via <stdfix.h> which is implemented accordingly with C Extensions to support embedded processors standard and GNU GCC manual.

The native fixed-point arithmetic adds:

• saturating arithmetic;
• fixed-point arithmetic;
• Rounding is not considered by the compiler, and it will always be done as specified in ARC's auxiliary register DSP_CTRL;
• prefix and postfix increment and decrement operators (++, --);
• unary arithmetic operators (+, -, !);
• binary arithmetic operators (+, -, *, /);
• binary shift operators (<<, >>);
• relational operators (<, <=, >=, >);
• equality operators (==, !=);
• assignment operators (+=, -=, *=, /=, <<=, >>=);
• conversions to and from integer, floating-point, or fixed-point types.

For more, see GNU GCC manual.

Directly mapped ARC' DSP instructions.

Mode	plus	minus	mul	div	lshft	rshft
q15	X	X	X	X	X	X
sat q15	VADDS2H	VSUBS2H	VMPY2HF	X	VASLS2H	VASRS2H
q31	X	X	X	DIVF	X	X
sat q31	ADDS	SUBS	MPYF	X	ASLS	ASRS
q63	X	X	X	X	X	X
sat q63	SATF	SATF	X	X	X	X
a32	X	X	X	X	X	X
sat a31	X	X	X	X	X	X

Smart builtins.

Name	rtl	instruction
abssh	ss_abs	ABSSH
abss	ss_abs	ABSS