[ARC] Fix decoding of w6 signed short immediate.

gas/
  Claudiu Zissulescu  <claziss@synopsys.com>

        * testsuite/gas/arc/st.d: Fix test.

opcodes/
  Claudiu Zissulescu  <claziss@synopsys.com>

        * arc-opc.c (extract_w6): Fix extending the sign.

gas/ChangeLog

@@ -1,3 +1,7 @@
+2018-07-23  Claudiu Zissulescu <claziss@synopsys.com>
+
+	* testsuite/gas/arc/st.d: Fix test.
+
 2018-07-23  Claudiu Zissulescu <claziss@synopsys.com>
 
 	* config/tc-arc.c (tokenize_extinsn): Convert to lower case the

gas/testsuite/gas/arc/st.d

@@ -13,7 +13,7 @@ Disassembly of section .text:
   10:	1a02 004c           	st[hw]+.aw	r1,\[r2,2\]
   14:	1e00 7040 0000 0384 	st	r1,\[0x384\]
   1c:	1a00 0003           	stb	0,\[r2\]
-  20:	1af8 8e01           	st	56,\[r2,-8\]
+  20:	1af8 8e01           	st	-8,\[r2,-8\]
   24:	1e00 7080 0000 0000 	st	r2,\[0\]
 			28: R_ARC_32_ME	foo
   2c:	1a02 0060           	st.di	r1,\[r2,2\]

opcodes/ChangeLog

@@ -1,3 +1,7 @@
+2018-07-23  Claudiu Zissulescu <claziss@synopsys.com>
+
+	* arc-opc.c (extract_w6): Fix extending the sign.
+
 2018-07-23  Claudiu Zissulescu <claziss@synopsys.com>
 
 	* arc-tbl.h (vewt): Allow it for ARC EM family.

opcodes/arc-opc.c

@@ -651,10 +651,14 @@ static long long
 extract_w6 (unsigned long long  insn,
 	    bfd_boolean *       invalid ATTRIBUTE_UNUSED)
 {
-  unsigned value = 0;
+  int value = 0;
 
   value |= ((insn >> 6) & 0x003f) << 0;
 
+  /* Extend the sign.  */
+  int signbit = 1 << 5;
+  value = (value ^ signbit) - signbit;
+
   return value;
 }