Merge pull request #4797 from laytan/improve-abs-of-float

improve abs() on floats for more correct and faster results

2 files changed, 30 insertions, 2 deletions

diff --git a/src/check_builtin.cpp b/src/check_builtin.cpp
index 7d0ce3aef..5aa4cf027 100644
--- a/src/check_builtin.cpp
+++ b/src/check_builtin.cpp
@@ -3488,9 +3488,12 @@ gb_internal bool check_builtin_procedure(CheckerContext *c, Operand *operand, As
 			case ExactValue_Integer:
 				mp_abs(&operand->value.value_integer, &operand->value.value_integer);
 				break;
-			case ExactValue_Float:
-				operand->value.value_float = gb_abs(operand->value.value_float);
+			case ExactValue_Float: {
+				u64 abs = bit_cast<u64>(operand->value.value_float);
+				abs &= 0x7FFFFFFFFFFFFFFF;
+				operand->value.value_float = bit_cast<f64>(abs);
 				break;
+			}
 			case ExactValue_Complex: {
 				f64 r = operand->value.value_complex->real;
 				f64 i = operand->value.value_complex->imag;
diff --git a/src/llvm_backend_proc.cpp b/src/llvm_backend_proc.cpp
index 7e44a0046..e5c04852c 100644
--- a/src/llvm_backend_proc.cpp
+++ b/src/llvm_backend_proc.cpp
@@ -2174,7 +2174,32 @@ gb_internal lbValue lb_build_builtin_proc(lbProcedure *p, Ast *expr, TypeAndValu
 			case 128: return lb_emit_runtime_call(p, "abs_complex128", args);
 			}
 			GB_PANIC("Unknown complex type");
+		} else if (is_type_float(t)) {
+			bool little = is_type_endian_little(t) || (is_type_endian_platform(t) && build_context.endian_kind == TargetEndian_Little);
+			Type *t_unsigned = nullptr;
+			lbValue mask = {0};
+			switch (type_size_of(t)) {
+			case 2:
+				t_unsigned = t_u16;
+				mask = lb_const_int(p->module, t_unsigned, little ? 0x7FFF : 0xFF7F);
+				break;
+			case 4:
+				t_unsigned = t_u32;
+				mask = lb_const_int(p->module, t_unsigned, little ? 0x7FFFFFFF : 0xFFFFFF7F);
+				break;
+			case 8:
+				t_unsigned = t_u64;
+				mask = lb_const_int(p->module, t_unsigned, little ? 0x7FFFFFFFFFFFFFFF : 0xFFFFFFFFFFFFFF7F);
+				break;
+			default:
+				GB_PANIC("abs: unhandled float size");
+			}
+
+			lbValue as_unsigned = lb_emit_transmute(p, x, t_unsigned);
+			lbValue abs = lb_emit_arith(p, Token_And, as_unsigned, mask, t_unsigned);
+			return lb_emit_transmute(p, abs, t);
 		}
+
 		lbValue zero = lb_const_nil(p->module, t);
 		lbValue cond = lb_emit_comp(p, Token_Lt, x, zero);
 		lbValue neg = lb_emit_unary_arith(p, Token_Sub, x, t);