Prototyping sat_s64 add/sub procedures.

1 files changed, 89 insertions, 0 deletions

diff --git a/ttt.jai b/ttt.jai
index 9c7f948..60db8b7 100644
--- a/ttt.jai
+++ b/ttt.jai
@@ -1163,6 +1163,95 @@ read_enter_confirmation :: inline (row: int, style: int, message: string) -> boo
 }
 
 main :: () {
+
+    // value_a: s64 = 2;
+    // value_b: s64 = S64_MAX-1;
+    value_a: s64 = -2;
+    value_b: s64 = S64_MIN+1;
+    print(">%\n", S64_MAX);
+    argx :=  get_command_line_arguments();
+    if argx.count > 1
+        value_a = parse_int(*argx[1]);
+    if argx.count > 2
+        value_b = parse_int(*argx[2]);
+
+    result: s64 = ---;
+    flags: s64;// = ---;
+    #asm LAHF_SAHF { // TODO Remove LAHF_SAHF it not required.
+
+        // Code from https://locklessinc.com/articles/sat_arithmetic/
+
+        
+        // value_a === b;
+        // value_b === c;
+        // add     value_a, value_b;
+        // mov     result, value_a;
+
+        // Version 1
+        // mov     b: gpr === b, value_a;
+        // mov     c: gpr === c, value_b;
+        // add     b, c;
+        // mov     result, b;
+        // seto    flags;
+        // cmovns  b, c;
+
+//        s64b sat_adds64b(s64b x, s64b y)
+//        {
+//        	u64b ux = x;
+//        	u64b uy = y;
+//        	u64b res = ux + uy;
+//        	
+//        	ux = (ux >> 63) + LONG_MAX;
+//        	
+//        	/* Force compiler to use cmovns instruction */
+//        	if ((s64b) ((ux ^ uy) | ~(uy ^ res)) >= 0)
+//        	{
+//        		res = ux;
+//        	}
+//        		
+//        	return res;
+//        }
+        // Version 2 - WORKS
+        mov     d: gpr === d, 9223372036854775807;
+        mov     a: gpr === a, value_a;
+        mov     b: gpr === b, value_b;
+        add     a, b;
+        seto    flags;                  // Signal overflow.
+        mov     result, a;
+        mov     a, value_a;
+        shr     a, 63;
+        add     a, d;
+        mov     c: gpr, value_a;
+        xor     c, b;
+        xor     b, result;
+        not     b;
+        or      c, b;
+        test    c, c;
+        cmovns  result, a;
+
+//        s64b sat_subs64b(s64b x, s64b y)
+//        {
+//        	u64b ux = x;
+//        	u64b uy = y;
+//        	u64b res = ux - uy;
+//        	
+//        	ux = (ux >> 63) + LONG_MAX;
+//        	
+//        	/* Force compiler to use cmovns instruction */
+//        	if ((s64b)((ux ^ uy) & (ux ^ res)) < 0)
+//        	{
+//        		res = ux;
+//        	}
+//        		
+//        	return res;
+//        }
+        // TODO Use https://godbolt.org/ to help
+    	
+    }
+    print("% + % = %\n", value_a, value_b, result);
+    print("flag: %\n", flags);
+    return;
+    
     
     // TODO Implement signal handling and see modules/Debug.jai for examples.