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.y...@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
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