support for fixed size ints (all), but only BE

README.md

@@ -101,3 +101,26 @@ This __field annontation__ allows to store __integer fields__ of any size more c
 ## @FixedSize(size)
 
 Use it with fixed-size collections (like hashes, keys, etc) to not to keep collection size in the packed binary. It saves at least one byte.
+
+## @Fixed
+
+Can be used with any integer type to store/restor it as is, fixed-size, big-endian:
+
+- Short, UShort: 2 bytes
+- Int, UInt: 4 bytes
+- Long, ULong: 8 bytes
+
+Note that without this modifier all integers are serialized into variable-length compressed format, see class [Smartint] from this library.
+
+Example:
+~~~kotlin
+@Serializable
+class Foo(
+     @Fixed
+     val eightBytesLongInt: Long
+)
+
+// so:
+assertEquals("00 00 00 01 00 00 00 02", BipackEncoder.encode(Foo(0x100000002)).encodeToHex())
+~~~
+

src/commonMain/kotlin/net.sergeych.bipack/BipackDecoder.kt

@@ -35,7 +35,9 @@ class BipackDecoder(
         if (fixedNumber) input.readI32()
         else if (nextIsUnsigned) input.readNumber<UInt>().toInt() else input.readNumber()
 
-    override fun decodeLong(): Long = if (nextIsUnsigned) input.readNumber<ULong>().toLong() else input.readNumber()
+    override fun decodeLong(): Long =
+        if( fixedNumber ) input.readI64()
+        else if (nextIsUnsigned) input.readNumber<ULong>().toLong() else input.readNumber()
     override fun decodeFloat(): Float = input.readFloat()
     override fun decodeDouble(): Double = input.readDouble()
     override fun decodeChar(): Char = Char(input.readNumber<UInt>().toInt())

src/commonMain/kotlin/net.sergeych.bipack/BipackEncoder.kt

@@ -44,7 +44,10 @@ class BipackEncoder(val output: DataSink) : AbstractEncoder() {
         else output.writeNumber(value)
 
     fun encodeUInt(value: UInt) = output.writeNumber(value)
-    override fun encodeLong(value: Long) = if (nextIsUnsigned)
+    override fun encodeLong(value: Long) =
+        if (fixedNumber)
+            output.writeI64(value)
+        else if (nextIsUnsigned)
             output.writeNumber(value.toULong())
         else
             output.writeNumber(value)

src/commonMain/kotlin/net.sergeych.bipack/annotations.kt

@@ -48,16 +48,47 @@ annotation class CrcProtected
 annotation class Unsigned
 
 /**
- * Use it with collection of fixed size, like hash digest, key bits and so on, by not storing collection
- * size. It effectively reduced packed size to at least one byte. depending on the actual
+ * Fixed size collection of a given size. __Use it only with collections!__
+ *
+ * Use it with collection of fixed size, to read/write exact number of items (for example, bytes),
+ * like hash digest, key bits and so on. Does not stores/loades the collection
+ * size what reduces packed size to at least one byte. depending on the actual
  * collection size. As for nowonly collection types (e.g. ByteArray, List<T>m etc) are supported.
  * Note that if the actual collection size differs from [size], [BipackEncoder] will throw
- * [WrongCollectionSize] while encoding it.
+ * [WrongCollectionSize] while encoding it. For example:
+ *
+ * ~~~
+ * @Serializable
+ * class Foo(
+ *      @FixedSize(32)
+ *      thirtyTwoBytes: ByteArray
+ * )
  */
 @SerialInfo
 @Target(AnnotationTarget.FIELD, AnnotationTarget.PROPERTY)
 annotation class FixedSize(val size: Int)
 
+/**
+ * Fixed-size number, big-endian. Could be used only with field of following types:
+ *
+ * - Int, UInt: 4 bytes
+ * - Short, UShort: 2 bytes
+ * - Long, ULong: 8 bytes.
+ *
+ * It should not be used with Byte or UByte as their size is always 1 byte ;)
+ *
+ * Example:
+ * ~~~
+ * @Serializable
+ * class Foo(
+ *      @Fixed
+ *      val eightBytesLongInt: Long
+ * )
+ *
+ * // so:
+ * assertEquals("00 00 00 01 00 00 00 02", BipackEncoder.encode(Foo(0x100000002)).encodeToHex())
+ * ~~~
+ */
 @SerialInfo
 @Target(AnnotationTarget.FIELD, AnnotationTarget.PROPERTY)
 annotation class Fixed

src/commonTest/kotlin/bipack/BipackEncoderTest.kt

@@ -223,7 +223,7 @@ class BipackEncoderTest {
     @Serializable
     data class Fixa(
         @FixedSize(5)
-        val x: ByteArray
+        val x: ByteArray,
     )
 
     @Test
@@ -307,8 +307,16 @@ class BipackEncoderTest {
     @Serializable
     data class FI16(@Fixed val i: Short)
 
+    @Serializable
+    data class FI64(@Fixed val i: Long)
+
     @Serializable
     data class FU16(@Fixed val i: UShort)
+    @Serializable
+    class Foo(
+        @Fixed
+        val eightBytesLongInt: Long,
+    )
 
     @Test
     fun testFixedInt() {
@@ -319,7 +327,18 @@ class BipackEncoderTest {
         assertEquals(-1, BipackEncoder.encode(FI32(-1)).decodeFromBipack<FI32>().i)
         assertEquals("FF FF FF FF", BipackEncoder.encode(FU32(0xFFFFFFFFu)).encodeToHex())
         assertEquals("FF 01 02 03", BipackEncoder.encode(FU32(0xFF010203u)).encodeToHex())
+
         assertEquals("FF 03", BipackEncoder.encode(FU16(0xFF03u)).encodeToHex())
         assertEquals(0x7ffeu, BipackEncoder.encode(FU16(0x7ffeu)).decodeFromBipack<FU16>().i)
+        assertEquals(-1, BipackEncoder.encode(FI16(-1)).decodeFromBipack<FI16>().i)
+        assertEquals(0x7ffe, BipackEncoder.encode(FI16(0x7ffe)).decodeFromBipack<FI16>().i)
+
+        assertEquals("00 00 00 01 00 00 00 02", BipackEncoder.encode(FI64(0x100000002)).encodeToHex())
+        assertEquals(0x100000002, BipackEncoder.encode(FI64(0x100000002)).decodeFromBipack<FI64>().i)
+
+
+        // so:
+        assertEquals("00 00 00 01 00 00 00 02", BipackEncoder.encode(Foo(0x100000002)).encodeToHex())
+
     }
 }