x86 gradient rounding implementation

mkeeter · May 12, 2024 · 9699faf · 9699faf
1 parent 22ff723
commit 9699faf
Showing 1 changed file with 21 additions and 13 deletions.
diff --git a/fidget/src/jit/x86_64/grad_slice.rs b/fidget/src/jit/x86_64/grad_slice.rs
@@ -262,24 +262,32 @@ impl Assembler for GradSliceAssembler {
         );
     }
 
-    // TODO hand-write these functions
     fn build_floor(&mut self, out_reg: u8, lhs_reg: u8) {
-        extern "sysv64" fn grad_floor(v: Grad) -> Grad {
-            v.floor()
-        }
-        self.call_fn_unary(out_reg, lhs_reg, grad_floor);
+        dynasm!(self.0.ops
+            ; vroundss xmm1, Rx(reg(lhs_reg)), Rx(reg(lhs_reg)), 1
+            ; vpxor Rx(reg(out_reg)), Rx(reg(out_reg)), Rx(reg(out_reg))
+            ; movss Rx(reg(out_reg)), xmm1
+        );
     }
     fn build_ceil(&mut self, out_reg: u8, lhs_reg: u8) {
-        extern "sysv64" fn grad_ceil(v: Grad) -> Grad {
-            v.ceil()
-        }
-        self.call_fn_unary(out_reg, lhs_reg, grad_ceil);
+        dynasm!(self.0.ops
+            ; vroundss xmm1, Rx(reg(lhs_reg)), Rx(reg(lhs_reg)), 2
+            ; vpxor Rx(reg(out_reg)), Rx(reg(out_reg)), Rx(reg(out_reg))
+            ; movss Rx(reg(out_reg)), xmm1
+        );
     }
     fn build_round(&mut self, out_reg: u8, lhs_reg: u8) {
-        extern "sysv64" fn grad_round(v: Grad) -> Grad {
-            v.round()
-        }
-        self.call_fn_unary(out_reg, lhs_reg, grad_round);
+        // Shenanigans figured through Godbolt
+        dynasm!(self.0.ops
+            ; mov eax, 0x80000000u32 as i32
+            ; vmovd xmm1, eax
+            ; vandps  xmm1, xmm1, Rx(reg(lhs_reg))
+            ; mov eax, 0x3effffffu32 as i32
+            ; vmovd xmm2, eax
+            ; vorps  xmm1, xmm1, xmm2
+            ; vaddss Rx(reg(out_reg)), xmm1, Rx(reg(lhs_reg))
+            ; vroundss Rx(reg(out_reg)), Rx(reg(out_reg)), Rx(reg(out_reg)), 3
+        );
     }
 
     fn build_add(&mut self, out_reg: u8, lhs_reg: u8, rhs_reg: u8) {