Add function to round numbers for 32-bit float storage

Author: kriszyp

README.md

@@ -180,6 +180,8 @@ const { ALWAYS, DECIMAL_ROUND, DECIMAL_FIT } = FLOAT32_OPTIONS;
 
 Note, that the performance is decreased with decimal rounding by about 20-25%, although if only 5% of your values are floating point, that will only have about a 1% impact overall.
 
+In addition, msgpackr exports a `roundFloat32(number)` function that can be used to round floating point numbers to the maximum significant decimal digits that can be stored in 32-bit float, just as DECIMAL_ROUND does when encoding. This can be useful for determine how a number will be stored prior to encoding it.
+
 ## Performance
 Msgpackr is fast. Really fast. Here is comparison with the next fastest JS projects using the benchmark tool from `msgpack-lite` (and the sample data is from some clinical research data we use that has a good mix of different value types and structures). It also includes comparison to V8 native JSON functionality, and JavaScript Avro (`avsc`, a very optimized Avro implementation):
 

index.js

@@ -1,5 +1,5 @@
 export { Packr, Encoder, addExtension, pack, encode, NEVER, ALWAYS, DECIMAL_ROUND, DECIMAL_FIT } from './pack.js'
-export { Unpackr, Decoder, C1, unpack, unpackMultiple, decode, FLOAT32_OPTIONS, clearSource } from './unpack.js'
+export { Unpackr, Decoder, C1, unpack, unpackMultiple, decode, FLOAT32_OPTIONS, clearSource, roundFloat32 } from './unpack.js'
 export { decodeIter, encodeIter } from './iterators.js'
 export const useRecords = false
 export const mapsAsObjects = true

node-index.js

@@ -1,5 +1,5 @@
 export { Packr, Encoder, addExtension, pack, encode, NEVER, ALWAYS, DECIMAL_ROUND, DECIMAL_FIT } from './pack.js'
-export { Unpackr, Decoder, C1, unpack, unpackMultiple, decode, FLOAT32_OPTIONS, clearSource} from './unpack.js'
+export { Unpackr, Decoder, C1, unpack, unpackMultiple, decode, FLOAT32_OPTIONS, clearSource, roundFloat32 } from './unpack.js'
 export { PackrStream, UnpackrStream, PackrStream as EncoderStream, UnpackrStream as DecoderStream } from './stream.js'
 export { decodeIter, encodeIter } from './iterators.js'
 export const useRecords = false

pack.js

@@ -273,7 +273,7 @@ export class Packr extends Unpackr {
 						targetView.setFloat32(position, value)
 						let xShifted
 						if (useFloat32 < 4 ||
-							// this checks for  rounding of numbers that were encoded in 32-bit float to nearest significant decimal digit that could be preserved
+								// this checks for rounding of numbers that were encoded in 32-bit float to nearest significant decimal digit that could be preserved
 								((xShifted = value * mult10[((target[position] & 0x7f) << 1) | (target[position + 1] >> 7)]) >> 0) === xShifted) {
 							position += 4
 							return

package.json

@@ -1,7 +1,7 @@
 {
   "name": "msgpackr",
   "author": "Kris Zyp",
-  "version": "1.4.3",
+  "version": "1.4.4",
   "description": "Ultra-fast MessagePack implementation with extensions for records and structured cloning",
   "license": "MIT",
   "types": "./index.d.ts",
@@ -47,7 +47,7 @@
     }
   },
   "optionalDependencies": {
-    "msgpackr-extract": "^1.0.13"
+    "msgpackr-extract": "^1.0.14"
   },
   "devDependencies": {
     "@rollup/plugin-json": "^4.1.0",

tests/test.js

@@ -15,6 +15,7 @@ var assert = chai.assert
 var Packr = msgpackr.Packr
 var unpack = msgpackr.unpack
 var unpackMultiple = msgpackr.unpackMultiple
+var roundFloat32 = msgpackr.roundFloat32
 var pack = msgpackr.pack
 var DECIMAL_FIT = msgpackr.FLOAT32_OPTIONS.DECIMAL_FIT
 
@@ -531,6 +532,11 @@ suite('msgpackr basic tests', function(){
 		assert.isTrue(deserialized.tooBig > 2n**65n)
 	})
 
+	test('roundFloat32', function() {
+		assert.equal(roundFloat32(0.00333000003), 0.00333)
+		assert.equal(roundFloat32(43.29999999993), 43.3)
+	})
+
 	test('buffers', function(){
 		var data = {
 			buffer1: new Uint8Array([2,3,4]),

unpack.d.ts

@@ -40,4 +40,5 @@ export function unpackMultiple(messagePack: Buffer | Uint8Array, forEach?: (valu
 export function decode(messagePack: Buffer | Uint8Array): any
 export function addExtension(extension: Extension): void
 export function clearSource(): void
+export function roundFloat32(float32Number: number): number
 export const C1: {}

unpack.js

@@ -964,3 +964,10 @@ export const FLOAT32_OPTIONS = {
 	DECIMAL_ROUND: 3,
 	DECIMAL_FIT: 4
 }
+let f32Array = new Float32Array(1)
+let u8Array = new Uint8Array(f32Array.buffer, 0, 4)
+export function roundFloat32(float32Number) {
+	f32Array[0] = float32Number
+	let multiplier = mult10[((u8Array[3] & 0x7f) << 1) | (u8Array[2] >> 7)]
+	return ((multiplier * float32Number + (float32Number > 0 ? 0.5 : -0.5)) >> 0) / multiplier
+}