fix negative offsets

Author: mhr3

x86/x86asm/decode.go

@@ -537,7 +537,7 @@ Decode:
 						if pos+2 > len(src) {
 							return truncated(src, mode)
 						}
-						mem.Disp = int64(binary.LittleEndian.Uint16(src[pos:]))
+						mem.Disp = int64(int16(binary.LittleEndian.Uint16(src[pos:])))
 						pos += 2
 					}
 
@@ -611,7 +611,7 @@ Decode:
 					}
 					dispoff = pos
 					displen = 4
-					mem.Disp = int64(binary.LittleEndian.Uint32(src[pos:]))
+					mem.Disp = int64(int32(binary.LittleEndian.Uint32(src[pos:])))
 					pos += 4
 				}
 

x86/x86asm/testdata/decode.txt

@@ -4417,6 +4417,9 @@
 668d11|223344556677885f5f5f5f5f5f	64	gnu	lea (%rcx),%dx
 668d11|223344556677885f5f5f5f5f5f	64	intel	lea dx, ptr [rcx]
 668d11|223344556677885f5f5f5f5f5f	64	plan9	LEAW 0(CX), DX
+8d8f0f00ffff|556677885f5f5f5f5f5f	64	intel	lea ecx, ptr [rdi-0xfff1]
+8d8f0f00ffff|556677885f5f5f5f5f5f	64	plan9	LEAL -0xfff1(DI), CX
+8d8f0f00ffff|556677885f5f5f5f5f5f	64	gnu	lea -0xfff1(%rdi),%ecx
 668ec0|11223344556677885f5f5f5f5f	32	intel	mov es, ax
 668ec0|11223344556677885f5f5f5f5f	32	plan9	MOVW AX, ES
 668ec0|11223344556677885f5f5f5f5f	64	gnu	mov %ax,%es
@@ -6773,6 +6776,9 @@ c441305ec2|556677885f5f5f5f5f5f5f	64	gnu	vdivps %xmm10,%xmm9,%xmm8
 c4c17a1009|556677885f5f5f5f5f5f5f	64	intel	vmovss xmm1, dword ptr [r9]
 c4c17a1009|556677885f5f5f5f5f5f5f	64	plan9	VMOVSS 0(R9), X1
 c4c17a1009|556677885f5f5f5f5f5f5f	64	gnu	vmovss (%r9),%xmm1
+c4817a11048a|6677885f5f5f5f5f5f5f	64	intel	vmovss dword ptr [r10+r9*4], xmm0
+c4817a11048a|6677885f5f5f5f5f5f5f	64	plan9	VMOVSS X0, 0(R10)(R9*4)
+c4817a11048a|6677885f5f5f5f5f5f5f	64	gnu	vmovss %xmm0,(%r10,%r9,4)
 c5f5efe2|44556677885f5f5f5f5f5f5f	64	intel	vpxor ymm4, ymm1, ymm2
 c5f5efe2|44556677885f5f5f5f5f5f5f	64	plan9	VPXOR Y2, Y1, Y4
 c5f5efe2|44556677885f5f5f5f5f5f5f	64	gnu	vpxor %ymm2,%ymm1,%ymm4