go full-on aarch64 mode, with clang as the default (and only supported) compiler

build.sh

@@ -30,7 +30,7 @@ then
 fi
 
 mkdir -p bin
-CC="${CC:-cc}"
+CC="${CC:-clang}"
 CFLAGS="${CFLAGS:--std=c89 -Wall -Wno-unknown-pragmas}"
 case "$(uname -s 2>/dev/null)" in
 MSYS_NT*|MINGW*) # MSYS2 on Windows

src/devices/ppu_aarch64.c

@@ -0,0 +1,31 @@
+#include <arm_neon.h>
+#include "ppu.h"
+
+void
+ppu_redraw(Ppu *p, Uint32 *screen)
+{
+	uint8x16x4_t pal = vld4q_u8((Uint8*)p->palette);
+	Uint8 *fg = p->fg.pixels;
+	Uint8 *bg = p->bg.pixels;
+	int i;
+
+	p->fg.changed = p->bg.changed = 0;
+
+	__builtin_assume(p->width > 0 && p->height > 0);
+
+	for(i = 0; i < (p->width * p->height & ~15); i += 16, fg += 16, bg += 16, screen += 16) {
+		uint8x16_t fg8 = vld1q_u8(fg);
+		uint8x16_t bg8 = vld1q_u8(bg);
+		uint8x16_t px8 = vbslq_u8(vceqzq_u8(fg8), bg8, fg8);
+		uint8x16x4_t px = {
+			vqtbl1q_u8(pal.val[0], px8),
+			vqtbl1q_u8(pal.val[1], px8),
+			vqtbl1q_u8(pal.val[2], px8),
+			vdupq_n_u8(0xff),
+		};
+		vst4q_u8((uint8_t*)screen, px);
+	}
+
+	for(; i < p->width * p->height; i++)
+		screen[i] = p->palette[*fg ? *fg : *bg];
+}