Implement support for 64-bit builds.

The implentation is through a few macros to handle the fact in 64-bit, all addresses have to be loaded first to register and only offsets are ok. Also, push only supports 64-bit registers in 64-bit, so we have _AX, _BX, _CX etc. defines, which are eax, ebx and ecx on 32bit and rax, rbx and rcx on 64bit.

src/win64/gmdls_win64.asm

@@ -0,0 +1,44 @@
+%ifdef INCLUDE_GMDLS
+
+%define SAMPLE_TABLE_SIZE 3440660 ; size of gmdls
+
+extern OpenFile ; requires windows
+extern ReadFile ; requires windows
+
+SECT_TEXT(sugmdls)
+;        Win64 ABI: RCX, RDX, R8, and R9
+su_gmdls_load:
+    sub     rsp, 40         ; Win64 ABI requires "shadow space" + space for one parameter.
+    mov     rdi, PTRWORD MANGLE_DATA(su_sample_table)
+    mov     rsi, PTRWORD su_gmdls_path1
+    su_gmdls_pathloop:
+        xor     r8,r8 ; OF_READ
+        mov     rdx, rdi             ; &ofstruct, blatantly reuse the sample table
+        mov     rcx, rsi        ; path
+        call    OpenFile            ; eax = OpenFile(path,&ofstruct,OF_READ)
+        add     rsi, su_gmdls_path2 - su_gmdls_path1 ; if we ever get to third, then crash
+        movsxd  rcx,eax
+        cmp     rcx, -1             ; ecx == INVALID?
+        je      su_gmdls_pathloop
+    mov     qword [rsp+32],0
+    mov     r9, rdi
+    mov     r8d, SAMPLE_TABLE_SIZE   ; number of bytes to read
+    mov     rdx, rdi
+    call    ReadFile                ; Readfile(handle,&su_sample_table,SAMPLE_TABLE_SIZE,&bytes_read,NULL)
+    add     rsp, 40         ; shadow space, as required by Win64 ABI
+    ret
+
+SECT_DATA(sugmpath)
+
+su_gmdls_path1:
+    db 'drivers/gm.dls',0
+su_gmdls_path2:
+    db 'drivers/etc/gm.dls',0
+
+SECT_DATA(suconst)
+    c_samplefreq_scaling    dd      84.28074964676522       ; o = 0.000092696138, n = 72, f = 44100*o*2**(n/12), scaling = 22050/f <- so note 72 plays at the "normal rate"
+
+SECT_BSS(susamtbl)
+    EXPORT MANGLE_DATA(su_sample_table)    resb    SAMPLE_TABLE_SIZE    ; size of gmdls.
+
+%endif