Reduce error to 4ULP.

Author: calder

library/std/tests/floats/f16.rs

@@ -961,9 +961,9 @@ fn test_algebraic() {
 
     assert_approx_eq!(a.algebraic_add(b), a + b, 1e1);
     assert_approx_eq!(a.algebraic_sub(b), a - b, 1e1);
-    assert_approx_eq!(a.algebraic_mul(b), a * b, 1e3);
-    assert_approx_eq!(a.algebraic_div(b), a / b, 1e-2);
-    assert_approx_eq!(a.algebraic_rem(b), a % b, 1e1);
+    assert_approx_eq!(a.algebraic_mul(b), a * b, 1e2);
+    assert_approx_eq!(a.algebraic_div(b), a / b, 1e0);
+    assert_approx_eq!(a.algebraic_rem(b), a % b, 1e0);
 }
 
 #[test]

library/std/tests/floats/f32.rs

@@ -921,9 +921,9 @@ fn test_algebraic() {
     let a: f32 = 123.0;
     let b: f32 = 456.0;
 
-    assert_approx_eq!(a.algebraic_add(b), a + b, 1e-2);
-    assert_approx_eq!(a.algebraic_sub(b), a - b, 1e-2);
+    assert_approx_eq!(a.algebraic_add(b), a + b, 1e-3);
+    assert_approx_eq!(a.algebraic_sub(b), a - b, 1e-3);
     assert_approx_eq!(a.algebraic_mul(b), a * b, 1e-1);
-    assert_approx_eq!(a.algebraic_div(b), a / b, 1e-5);
-    assert_approx_eq!(a.algebraic_rem(b), a % b, 1e-2);
+    assert_approx_eq!(a.algebraic_div(b), a / b, 1e-4);
+    assert_approx_eq!(a.algebraic_rem(b), a % b, 1e-4);
 }

src/tools/miri/src/intrinsics/mod.rs

@@ -411,9 +411,9 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
                 };
                 let res = this.binary_op(op, &a, &b)?;
                 // `binary_op` already called `generate_nan` if needed.
-                // Apply a relative error of 16ULP to simulate non-deterministic precision loss
+                // Apply a relative error of 4ULP to simulate non-deterministic precision loss
                 // due to optimizations.
-                let res = apply_random_float_error_to_imm(this, res, 4 /* log2(16) */)?;
+                let res = apply_random_float_error_to_imm(this, res, 2 /* log2(4) */)?;
                 this.write_immediate(*res, dest)?;
             }
 
@@ -464,9 +464,9 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
                 if !float_finite(&res)? {
                     throw_ub_format!("`{intrinsic_name}` intrinsic produced non-finite value as result");
                 }
-                // Apply a relative error of 16ULP to simulate non-deterministic precision loss
+                // Apply a relative error of 4ULP to simulate non-deterministic precision loss
                 // due to optimizations.
-                let res = apply_random_float_error_to_imm(this, res, 4 /* log2(16) */)?;
+                let res = apply_random_float_error_to_imm(this, res, 2 /* log2(4) */)?;
                 this.write_immediate(*res, dest)?;
             }