Floating-point rounding instructions (#232)

New floating-point rounding instructions:

- Round to nearest integer, ties to even: `f32x4.nearest`/`f64x2.nearest`
- Round to integer towards zero (truncate to integer): `f32x4.trunc`/`f64x2.trunc`
- Round to integer above (ceiling): `f32x4.ceil`/`f64x2.ceil`
- Round to integer below (floor): `f32x4.floor`/`f64x2.floor`

Author: Maratyszcza

proposals/simd/BinarySIMD.md

@@ -188,6 +188,14 @@ For example, `ImmLaneIdx16` is a byte with values in the range 0-15 (inclusive).
 | `i64x2.add`                |    `0xce`| -                  |
 | `i64x2.sub`                |    `0xd1`| -                  |
 | `i64x2.mul`                |    `0xd5`| -                  |
+| `f32x4.ceil`               |    `0xd8`| -                  |
+| `f32x4.floor`              |    `0xd9`| -                  |
+| `f32x4.trunc`              |    `0xda`| -                  |
+| `f32x4.nearest`            |    `0xdb`| -                  |
+| `f64x2.ceil`               |    `0xdc`| -                  |
+| `f64x2.floor`              |    `0xdd`| -                  |
+| `f64x2.trunc`              |    `0xde`| -                  |
+| `f64x2.nearest`            |    `0xdf`| -                  |
 | `f32x4.abs`                |    `0xe0`| -                  |
 | `f32x4.neg`                |    `0xe1`| -                  |
 | `f32x4.sqrt`               |    `0xe3`| -                  |

proposals/simd/ImplementationStatus.md

@@ -165,6 +165,10 @@
 | `f32x4.div`                |               `-msimd128` | :heavy_check_mark: |                    |                    | :heavy_check_mark: |
 | `f32x4.min`                |               `-msimd128` | :heavy_check_mark: |                    |                    | :heavy_check_mark: |
 | `f32x4.max`                |               `-msimd128` | :heavy_check_mark: |                    |                    | :heavy_check_mark: |
+| `f32x4.ceil`               |                           |                    |                    |                    |                    |
+| `f32x4.floor`              |                           |                    |                    |                    |                    |
+| `f32x4.trunc`              |                           |                    |                    |                    |                    |
+| `f32x4.nearest`            |                           |                    |                    |                    |                    |
 | `f64x2.abs`                |               `-msimd128` | :heavy_check_mark: |                    |                    | :heavy_check_mark: |
 | `f64x2.neg`                |               `-msimd128` | :heavy_check_mark: |                    |                    | :heavy_check_mark: |
 | `f64x2.sqrt`               |               `-msimd128` | :heavy_check_mark: |                    |                    | :heavy_check_mark: |
@@ -174,6 +178,10 @@
 | `f64x2.div`                |               `-msimd128` | :heavy_check_mark: |                    |                    | :heavy_check_mark: |
 | `f64x2.min`                |               `-msimd128` | :heavy_check_mark: |                    |                    | :heavy_check_mark: |
 | `f64x2.max`                |               `-msimd128` | :heavy_check_mark: |                    |                    | :heavy_check_mark: |
+| `f64x2.ceil`               |                           |                    |                    |                    |                    |
+| `f64x2.floor`              |                           |                    |                    |                    |                    |
+| `f64x2.trunc`              |                           |                    |                    |                    |                    |
+| `f64x2.nearest`            |                           |                    |                    |                    |                    |
 | `i32x4.trunc_sat_f32x4_s`  |               `-msimd128` | :heavy_check_mark: |                    |                    | :heavy_check_mark: |
 | `i32x4.trunc_sat_f32x4_u`  |               `-msimd128` | :heavy_check_mark: |                    |                    | :heavy_check_mark: |
 | `f32x4.convert_i32x4_s`    |               `-msimd128` | :heavy_check_mark: |                    |                    | :heavy_check_mark: |

proposals/simd/SIMD.md

@@ -914,6 +914,30 @@ Lane-wise IEEE `multiplication`.
 
 Lane-wise IEEE `squareRoot`.
 
+### Round to integer above (ceiling)
+* `f32x4.ceil(a: v128) -> v128`
+* `f64x2.ceil(a: v128) -> v128`
+
+Lane-wise rounding to the nearest integral value not smaller than the input.
+
+### Round to integer below (floor)
+* `f32x4.floor(a: v128) -> v128`
+* `f64x2.floor(a: v128) -> v128`
+
+Lane-wise rounding to the nearest integral value not greater than the input.
+
+### Round to integer toward zero (truncate to integer)
+* `f32x4.trunc(a: v128) -> v128`
+* `f64x2.trunc(a: v128) -> v128`
+
+Lane-wise rounding to the nearest integral value with the magnitude not larger than the input.
+
+### Round to nearest integer, ties to even
+* `f32x4.nearest(a: v128) -> v128`
+* `f64x2.nearest(a: v128) -> v128`
+
+Lane-wise rounding to the nearest integral value; if two values are equally near, rounds to the even one.
+
 ## Conversions
 ### Integer to floating point
 * `f32x4.convert_i32x4_s(a: v128) -> v128`