Merge pull request #6 from riscv/5-scaled-offsets-for-compressed-enco…

…dings

Making the address computation for C.SD and C.LD explicit

zilsd.adoc

@@ -25,10 +25,12 @@ If the C extension is present and F is not present, Zilsd adds the following RV3
 
   - C.LDSP loads stack-pointer relative 64-bit value into registers `rd'` and `rd'+1`. It computes its effective address by adding the zero-extended offset, scaled by 8, to the stack pointer, `x2`. It expands to `ld rd, offset(x2)`. C.LDSP is only valid when _rd_≠x0; the code points with _rd_=x0 are reserved.
   - C.SDSP stores a stack-pointer relative 64-bit value from registers `rs2'` and `rs2'+1`. It computes an effective address by adding the _zero_-extended offset, scaled by 8, to the stack pointer, `x2`. It expands to `sd rs2, offset(x2)`.
-  - C.LD loads a 64-bit value into registers `rd'` and `rd'+1`. It expands to
-  `ld rd', offset(rs1')`.
-  - C.SD stores a 64-bit value from registers `rs2'` and `rs2'+1`. It expands to
-  `sd rs2', offset(rs1')`.
+  - C.LD loads a 64-bit value into registers `rd'` and `rd'+1`.
+  It computes an effective address by adding the zero-extended offset, scaled by 8, to the base address in register rs1'.
+  It expands to `ld rd', offset(rs1')`.
+  - C.SD stores a 64-bit value from registers `rs2'` and `rs2'+1`.
+  It computes an effective address by adding the zero-extended offset, scaled by 8, to the base address in register rs1'.
+  It expands to `sd rs2', offset(rs1')`.
 
 These instructions are mutually exclusive with Zcf.