[FFmpeg-devel] [PATCH v3 2/4] libavutils: Add parse_r helper for MIPS

[Jiaxun Yang]

That helper grab from kernel code can allow us to inline
newer instructions (not implemented by the assembler) in
a elegant manner.

Signed-off-by: Jiaxun Yang <jiaxun.yang at flygoat.com>
---
 libavutil/mips/asmdefs.h | 42 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 42 insertions(+)

diff --git a/libavutil/mips/asmdefs.h b/libavutil/mips/asmdefs.h
index 748119918a..7e0e4cf575 100644
--- a/libavutil/mips/asmdefs.h
+++ b/libavutil/mips/asmdefs.h
@@ -55,4 +55,46 @@
 # define PTR_SLL        "sll "
 #endif
 
+/*
+ * parse_r var, r - Helper assembler macro for parsing register names.
+ *
+ * This converts the register name in $n form provided in \r to the
+ * corresponding register number, which is assigned to the variable \var. It is
+ * needed to allow explicit encoding of instructions in inline assembly where
+ * registers are chosen by the compiler in $n form, allowing us to avoid using
+ * fixed register numbers.
+ *
+ * It also allows newer instructions (not implemented by the assembler) to be
+ * transparently implemented using assembler macros, instead of needing separate
+ * cases depending on toolchain support.
+ *
+ * Simple usage example:
+ * __asm__ __volatile__("parse_r __rt, %0\n\t"
+ *			".insn\n\t"
+ *			"# di    %0\n\t"
+ *			".word   (0x41606000 | (__rt << 16))"
+ *			: "=r" (status);
+ */
+
+/* Match an individual register number and assign to \var */
+#define _IFC_REG(n)				\
+	".ifc	\\r, $" #n "\n\t"		\
+	"\\var	= " #n "\n\t"			\
+	".endif\n\t"
+
+__asm__(".macro	parse_r var r\n\t"
+	"\\var	= -1\n\t"
+	_IFC_REG(0)  _IFC_REG(1)  _IFC_REG(2)  _IFC_REG(3)
+	_IFC_REG(4)  _IFC_REG(5)  _IFC_REG(6)  _IFC_REG(7)
+	_IFC_REG(8)  _IFC_REG(9)  _IFC_REG(10) _IFC_REG(11)
+	_IFC_REG(12) _IFC_REG(13) _IFC_REG(14) _IFC_REG(15)
+	_IFC_REG(16) _IFC_REG(17) _IFC_REG(18) _IFC_REG(19)
+	_IFC_REG(20) _IFC_REG(21) _IFC_REG(22) _IFC_REG(23)
+	_IFC_REG(24) _IFC_REG(25) _IFC_REG(26) _IFC_REG(27)
+	_IFC_REG(28) _IFC_REG(29) _IFC_REG(30) _IFC_REG(31)
+	".iflt	\\var\n\t"
+	".error	\"Unable to parse register name \\r\"\n\t"
+	".endif\n\t"
+	".endm");
+
 #endif /* AVCODEC_MIPS_ASMDEFS_H */
-- 
2.20.1