Rewrite the JDIMENSION argument management for x86 64-bit assembly to

simd/jcgryss2-64.asm

 ;
 ; jcgryss2-64.asm - grayscale colorspace conversion (64-bit SSE2)
 ;
 ; x86 SIMD extension for IJG JPEG library
 ; Copyright (C) 1999-2006, MIYASAKA Masaru.
 ; Copyright (C) 2011, D. R. Commander.
 ; For conditions of distribution and use, see copyright notice in jsimdext.inc
 ;
 ; This file should be assembled with NASM (Netwide Assembler),
 ; can *not* be assembled with Microsoft's MASM or any compatible
@@ skipping 32 matching lines @@
         push    rbp
         mov     rax,rsp                         ; rax = original rbp
         sub     rsp, byte 4
         and     rsp, byte (-SIZEOF_XMMWORD)     ; align to 128 bits
         mov     [rsp],rax
         mov     rbp,rsp                         ; rbp = aligned rbp
         lea     rsp, [wk(0)]
         collect_args
         push    rbx
 
-        mov     rcx, r10
+        mov     ecx, r10d
         test    rcx,rcx
         jz      near .return
 
         push    rcx
 
         mov rsi, r12
-        mov rcx, r13
+        mov ecx, r13d
         mov     rdi, JSAMPARRAY [rsi+0*SIZEOF_JSAMPARRAY]
         lea     rdi, [rdi+rcx*SIZEOF_JSAMPROW]
 
         pop     rcx
 
         mov rsi, r11
         mov     eax, r14d
         test    rax,rax
         jle     near .return
 .rowloop:
@@ skipping 284 matching lines @@
         pop     rbx
         uncollect_args
         mov     rsp,rbp         ; rsp <- aligned rbp
         pop     rsp             ; rsp <- original rbp
         pop     rbp
         ret
 
 ; For some reason, the OS X linker does not honor the request to align the
 ; segment unless we do this.
         align   16