Add GSS-derived characteristics, array fields, precise scaling

Bundled characteristics (191 -> 348):
- recover the Fitness Machine profile and other characteristics from the last
  published Bluetooth SIG characteristic XML (2017)
- add 139 characteristics derived from the current GATT Specification Supplement
  (the SIG retired the machine-readable characteristic XML ~2019); scalars are
  high fidelity, complex conditional/struct cases carry <!-- REVIEW --> markers

Parser:
- variable-length array fields via Field.repeats (0 = to end of data, N = fixed);
  the parser emits indexed holders Name[0], Name[1], ... (e.g. RR-Interval)
- register the GSS float type names medfloat16/medfloat32 (IEEE-11073 16/32-bit)

Numeric conversion:
- exact BigDecimal scaling: decimal exponent via scaleByPowerOfTen, binary
  exponent via exact powers of two, so getBigDecimal/getBigInteger no longer
  inherit the rounding error of Math.pow(10, e)
- simplify two's-complement int/long deserialization (same results)
- implement the previously-unsupported IEEE-11073 serialize + deserializeDouble

README refreshed: GSS provenance, array support; fixed stale links/paths.

Signed-off-by: Vlad Kolotoff <vkolotoff@pm.me>

Author: vkolotov

README.md

@@ -2,24 +2,34 @@
 
 A **simple** library/framework to work with Bluetooth Smart (BLE) GATT services and characteristics.
 
-Note: This is a fork from the no longer maintained project at https://github.com/sputnikdev/bluetooth-gatt-parser.
+> This is a fork of the no longer maintained project at
+> https://github.com/sputnikdev/bluetooth-gatt-parser.
+
+Parsing a standard characteristic (Battery Level, `0x2A19`) is a one-liner:
 
-Have a look at an example of parsing a standard characteristic ([Battery Level 0x2A19](https://www.bluetooth.com/specifications/gatt/viewer?attributeXmlFile=org.bluetooth.characteristic.battery_level.xml)) value:
 ```java
 BluetoothGattParserFactory.getDefault().parse("2A19", new byte[] {51}).get("Level").getInteger(null);
 ```
-This would print 51.
 
-**Features:**
+This prints `51`.
+
+## Features
+
+1. Ships the standard [Bluetooth SIG GATT services and characteristics](https://www.bluetooth.com/specifications/assigned-numbers/), plus a number
+   of characteristics recovered from the SIG's retired characteristic XML and
+   generated from the current [GATT Specification Supplement](https://www.bluetooth.com/specifications/gss/).
+2. Parses single- and multi-field characteristics into a user-friendly data format.
+3. Serializes (writes) single- and multi-field characteristics.
+4. Validates input against the GATT specification (format types and mandatory fields).
+5. Supports variable-length array fields (e.g. the RR-Interval list in Heart Rate Measurement).
+6. Extensible: user-defined services and characteristics via drop-in XML.
+7. Supports all defined [format types](https://www.bluetooth.com/specifications/assigned-numbers/), including the
+   IEEE-11073 `SFLOAT`/`FLOAT` (GSS `medfloat16`/`medfloat32`) types.
 
-1. Supports 99% of the existing/standard [GATT services and characteristics specifications](https://www.bluetooth.com/specifications/gatt).
-2. Parse/read single and multi field characteristics into a user-friendly data format.
-3. Writing single and multi field characteristics.
-4. Validating input data whether it conforms to GATT specifications (format types and mandatory fields).
-5. Extensibility. User defined services and characteristics.
-6. Support for all defined [format types](https://www.bluetooth.com/specifications/assigned-numbers/format-types).
+## Usage
+
+Add the Maven dependency:
 
-**Start using the library by including a maven dependency in your project:**
 ```xml
 <dependency>
   <groupId>org.openhab</groupId>
@@ -28,66 +38,72 @@ This would print 51.
 </dependency>
 ```
 
-A more complex example of parsing multi-field characteristics ([Heart Rate service](https://www.bluetooth.com/specifications/gatt/viewer?attributeXmlFile=org.bluetooth.service.heart_rate.xml)):
+Reading and writing multi-field characteristics:
 
 ```java
-// Getting a default implementation which is capable of reading/writing the standard GATT services and characteristics
+// A default parser that reads/writes the bundled standard GATT services and characteristics.
 BluetoothGattParser parser = BluetoothGattParserFactory.getDefault();
 
-// Reading Body Sensor Location (0x2A38) characteristic (sigle field)
-byte[] data = new byte[] {1}; // 1 == Chest
-GattResponse response = parser.parse("2A38", data);
-String sensorLocation = response.get("Body Sensor Location").getInteger(null); // prints 1 (Chest)
+// Read Body Sensor Location (0x2A38) — a single-field characteristic.
+GattResponse response = parser.parse("2A38", new byte[] {1}); // 1 == Chest
+int sensorLocation = response.get("Body Sensor Location").getInteger(null); // 1 (Chest)
 
-// Reading Heart Rate Measurement (0x2A37) characteristic (multi field)
-byte[] data = new byte[] {20, 74, 13, 3};
-GattResponse response = parser.parse("2A37", data);
-String heartRateValue = response.get("Heart Rate Measurement Value (uint8)").getInteger(null); // prints 74
-String rrIntervalValue = response.get("RR-Interval").getInteger(null); // prints 781
+// Read Heart Rate Measurement (0x2A37) — a multi-field characteristic.
+response = parser.parse("2A37", new byte[] {20, 74, 13, 3});
+int heartRate = response.get("Heart Rate Measurement Value (8 bit resolution)").getInteger(null); // 74
 
-// Writing Heart Rate Control Point (0x2A39) characteristic
+// Write Heart Rate Control Point (0x2A39).
 GattRequest request = parser.prepare("2A39");
-request.setField("Heart Rate Control Point", 1); // control value to be sent to a bluetooth device
+request.setField("Heart Rate Control Point", 1);
 byte[] data = parser.serialize(request);
 ```
 
-See more examples in the integration tests: [GenericCharacteristicParserIntegrationTest](src/test/java/org/bluetooth/gattparser/GenericCharacteristicParserIntegrationTest.java)
-
----
-**Extending the library with user defined services and characteristics**
+See more in the integration tests:
+[GenericCharacteristicParserIntegrationTest](src/test/java/org/openhab/bluetooth/gattparser/GenericCharacteristicParserIntegrationTest.java).
 
-The gatt-parser library is designed to be able to add support for some new custom services/characteristics or to override an existing ("approved") [service and characteristic](https://www.bluetooth.com/specifications/gatt). This can be done by just providing a new GATT XML file which specifies your service and characteristic (have a look at the standard definition for the [Battery Level characteristic](src/main/resources/gatt/characteristic/org.bluetooth.characteristic.battery_level.xml)). The library will read your custom files and build internal rules/conditions for parsing and serialization of your custom characteristics. This means you don't have to write any code to parse/serialize simple or complex custom characteristics.
+## Extending with user-defined services and characteristics
 
-_Loading XML GATT specification files (GATT-like specifications) from a folder:_
+The library can add support for custom services/characteristics, or override a
+bundled one, purely by providing a GATT XML file — no code required. See the
+bundled [Battery Level characteristic](src/main/resources/gatt/characteristic/org.bluetooth.characteristic.battery_level.xml)
+for the schema.
 
 ```java
 BluetoothGattParser parser = BluetoothGattParserFactory.getDefault();
-File extensionsFolderFile = new File(..);
-gattParser.loadExtensionsFromFolder(extensions);
+parser.loadExtensionsFromFolder(new File("/path/to/gatt-extensions"));
 ```
 
-**A custom parser can be added for a characteristic if you are not satisfied with the default one**
+If the generic parser is not enough for a given characteristic, register your own:
 
-See the default one for a hint and a reference: [GenericCharacteristicParser](src/main/java/org/bluetooth/gattparser/GenericCharacteristicParser.java)
 ```java
 BluetoothGattParser parser = BluetoothGattParserFactory.getDefault();
-CharacteristicParser customParser = new ...; // your own implementation
-parser.registerParser(CHARACTERISTIC_UUID, customParser);
+parser.registerParser(CHARACTERISTIC_UUID, myCustomParser);
 ```
 
----
-## Contribution
+## Bundled GATT specifications
+
+Each characteristic/service is one XML file under `src/main/resources/gatt/`. A
+build-time generator indexes them into `gatt_spec_registry.json` (the `type`
+attribute of each file must equal its filename).
 
-You are welcome to contribute to the project.
+The Bluetooth SIG **retired** the machine-readable characteristic XML repository
+around 2019. Since then it publishes the [GATT Specification Supplement (GSS)](https://www.bluetooth.com/specifications/gss/)
+as YAML, where the field structure is present but scaling/unit/presence are
+encoded as a rigid mini-grammar inside prose. The characteristics added here were
+derived from that GSS: scalars are high fidelity, while cases the prose cannot
+express unambiguously carry an inline `<!-- REVIEW -->` marker rather than a
+fabricated value.
 
-The build process is streamlined by using standard maven tools. 
+## Contribution
+
+Contributions are welcome. Build with Maven:
 
-To build the project with maven:
 ```bash
 mvn clean install
 ```
 
-To cut a new release and upload it to the Maven Central Repository:
+Cut a release to Maven Central:
+
 ```bash
 mvn release:prepare -B
 mvn release:perform

src/main/java/org/openhab/bluetooth/gattparser/FieldHolder.java

@@ -161,7 +161,7 @@ public Long getLong(Long def) {
     public BigInteger getBigInteger(BigInteger def) {
         BigDecimal result = new BigDecimalConverter(null).convert(BigDecimal.class, prepareValue());
         return result != null
-                ? result.multiply(BigDecimal.valueOf(getMultiplier()))
+                ? result.multiply(getMultiplierExact())
                         .add(BigDecimal.valueOf(getOffset())).setScale(0, RoundingMode.HALF_UP).toBigInteger()
                 : def;
     }
@@ -175,7 +175,7 @@ public BigInteger getBigInteger(BigInteger def) {
     public BigDecimal getBigDecimal(BigDecimal def) {
         BigDecimal result = new BigDecimalConverter(null).convert(BigDecimal.class, prepareValue());
         return result != null
-                ? result.multiply(BigDecimal.valueOf(getMultiplier()))
+                ? result.multiply(getMultiplierExact())
                 : def;
     }
 
@@ -585,6 +585,29 @@ private double getMultiplier() {
         return multiplier;
     }
 
+    /**
+     * Exact BigDecimal counterpart of {@link #getMultiplier()}. The decimal exponent is applied via
+     * {@link BigDecimal#scaleByPowerOfTen(int)} and the binary exponent via exact powers of two, so
+     * the BigDecimal paths do not inherit the rounding error of {@code Math.pow(10, e)}.
+     */
+    private BigDecimal getMultiplierExact() {
+        BigDecimal multiplier = BigDecimal.ONE;
+        if (field.getDecimalExponent() != null) {
+            multiplier = multiplier.scaleByPowerOfTen(field.getDecimalExponent());
+        }
+        if (field.getBinaryExponent() != null) {
+            int b = field.getBinaryExponent();
+            BigDecimal powerOfTwo = new BigDecimal(BigInteger.TWO.pow(Math.abs(b)));
+            multiplier = b >= 0
+                    ? multiplier.multiply(powerOfTwo)
+                    : multiplier.divide(powerOfTwo); // negative power of two is always exact (terminates in binary)
+        }
+        if (field.getMultiplier() != null && field.getMultiplier() != 0) {
+            multiplier = multiplier.multiply(BigDecimal.valueOf(field.getMultiplier()));
+        }
+        return multiplier;
+    }
+
     /**
      * Reads offset-to-be-added to field value received from request.
      * This is an extension to official GATT characteristic field specification, 

src/main/java/org/openhab/bluetooth/gattparser/GenericCharacteristicParser.java

@@ -90,6 +90,24 @@ public LinkedHashMap<String, FieldHolder> parse(Characteristic characteristic, b
                     continue;
                 }
                 FieldFormat fieldFormat = field.getFormat();
+                if (field.isRepeated()) {
+                    // Array field (GSS uint16[n] etc.): repeat the element either a fixed number
+                    // of times or, when repeats == 0, until the data is exhausted. Elements are
+                    // exposed as indexed holders "Name[0]", "Name[1]", ...
+                    int elementSize = fieldFormat.getSize();
+                    if (elementSize == FieldFormat.FULL_SIZE || elementSize <= 0) {
+                        throw new CharacteristicFormatException(
+                                "Repeated field \"" + field.getName() + "\" must have a fixed-size element format.");
+                    }
+                    int repeats = field.getRepeats();
+                    int index = 0;
+                    while (repeats == 0 ? offset + elementSize <= raw.length * 8 : index < repeats) {
+                        result.put(field.getName() + "[" + index + "]", parseField(field, raw, offset));
+                        offset += elementSize;
+                        index++;
+                    }
+                    continue;
+                }
                 result.put(field.getName(), parseField(field, raw, offset));
                 if (fieldFormat.getSize() == FieldFormat.FULL_SIZE) {
                     // full size field, e.g. a string

src/main/java/org/openhab/bluetooth/gattparser/num/IEEE11073FloatingPointNumberFormatter.java

@@ -82,23 +82,81 @@ public Float deserializeFloat(BitSet bits) {
 
     @Override
     public Double deserializeDouble(BitSet bits) {
-        throw new IllegalStateException("Operation not supported");
+        // IEEE-11073 defines no 64-bit form; the 32-bit FLOAT is the widest, decoded as a Double.
+        Float value = deserializeFloat(bits);
+        return value != null ? value.doubleValue() : null;
     }
 
 
     @Override
     public BitSet serializeSFloat(Float number) {
-        throw new IllegalStateException("Operation not supported");
+        return serialize(number, 12, 4, SFLOAT_NaN, SFLOAT_POSITIVE_INFINITY, SFLOAT_NEGATIVE_INFINITY);
     }
 
     @Override
     public BitSet serializeFloat(Float number) {
-        throw new IllegalStateException("Operation not supported");
+        return serialize(number, 24, 8, FLOAT_NaN, FLOAT_POSITIVE_INFINITY, FLOAT_NEGATIVE_INFINITY);
     }
 
     @Override
     public BitSet serializeDouble(Double number) {
-        throw new IllegalStateException("Operation not supported");
+        return serializeFloat(number != null ? number.floatValue() : null);
+    }
+
+    /**
+     * Encodes a decimal value as an IEEE-11073 SFLOAT/FLOAT: a two's-complement mantissa in the low
+     * {@code mantissaSize} bits and a base-10 exponent in the top {@code exponentSize} bits, laid out
+     * little-endian to match the deserialize path. The exponent is chosen so the mantissa fits its
+     * signed range while preserving as much precision as the format allows.
+     */
+    private BitSet serialize(Float number, int mantissaSize, int exponentSize,
+                             int nanMantissa, int posInfMantissa, int negInfMantissa) {
+        int mantissa;
+        int exponent = 0;
+        if (number == null || Float.isNaN(number)) {
+            mantissa = nanMantissa;
+        } else if (number == Float.POSITIVE_INFINITY) {
+            mantissa = posInfMantissa;
+        } else if (number == Float.NEGATIVE_INFINITY) {
+            mantissa = negInfMantissa;
+        } else {
+            long mantissaMax = (1L << (mantissaSize - 1)) - 1; // largest positive signed mantissa
+            long mantissaMin = -(1L << (mantissaSize - 1));
+            int expMax = (1 << (exponentSize - 1)) - 1;
+            int expMin = -(1 << (exponentSize - 1));
+            double value = number;
+            // Raise the exponent until the mantissa fits the signed range.
+            double scaled = value;
+            while ((Math.round(scaled) > mantissaMax || Math.round(scaled) < mantissaMin) && exponent < expMax) {
+                scaled /= 10.0;
+                exponent++;
+            }
+            // Lower the exponent to keep fractional precision while the mantissa still fits.
+            while (exponent > expMin) {
+                double finer = scaled * 10.0;
+                if (Math.round(finer) > mantissaMax || Math.round(finer) < mantissaMin) {
+                    break;
+                }
+                scaled = finer;
+                exponent--;
+            }
+            mantissa = (int) Math.round(scaled);
+        }
+
+        BitSet result = new BitSet(mantissaSize + exponentSize);
+        BitSet mantissaBits = twosComplementNumberFormatter.serialize(mantissa, mantissaSize, true);
+        BitSet exponentBits = twosComplementNumberFormatter.serialize(exponent, exponentSize, true);
+        for (int i = 0; i < mantissaSize; i++) {
+            if (mantissaBits.get(i)) {
+                result.set(i);
+            }
+        }
+        for (int i = 0; i < exponentSize; i++) {
+            if (exponentBits.get(i)) {
+                result.set(mantissaSize + i);
+            }
+        }
+        return result;
     }
 
 }

src/main/java/org/openhab/bluetooth/gattparser/num/TwosComplementNumberFormatter.java

@@ -33,42 +33,37 @@ public Integer deserializeInteger(BitSet bits, int size, boolean signed) {
         if (size > 32) {
             throw new IllegalArgumentException("size must be less or equal 32");
         }
-
-        if (size == 1) {
-            signed = false;
-        }
-
-        boolean isNegative = signed && size > 1 && bits.get(size - 1);
-        int value = isNegative ? -1 : 0;
-        for (int i = 0; i < bits.length() && i < size; i++) {
-            if (isNegative && !bits.get(i)) {
-                value ^= 1 << i;
-            } else if (!isNegative && bits.get(i)) {
-                value |= 1 << i;
-            }
-        }
-        return value;
+        return (int) deserialize(bits, size, signed);
     }
 
     @Override
     public Long deserializeLong(BitSet bits, int size, boolean signed) {
         if (size > 64) {
             throw new IllegalArgumentException("size must be less or equal than 64");
         }
+        return deserialize(bits, size, signed);
+    }
 
+    /**
+     * Reads up to 64 bits, little-endian, into a long and sign-extends when required. The BitSet
+     * already holds the bits little-endian (bit 0 = LSB), so a straight accumulation of the low
+     * {@code size} bits yields the unsigned magnitude; a set top bit under two's-complement is then
+     * extended into the unused high bits.
+     */
+    private long deserialize(BitSet bits, int size, boolean signed) {
         if (size == 1) {
             signed = false;
         }
-
-        boolean isNegative = signed && size > 1 && bits.get(size - 1);
-        long value = isNegative ? -1L : 0L;
-        for (int i = 0; i < bits.length() && i < size; i++) {
-            if (isNegative && !bits.get(i)) {
-                value ^= 1L << i;
-            } else if (!isNegative && bits.get(i)) {
+        long value = 0L;
+        int limit = Math.min(size, bits.length());
+        for (int i = 0; i < limit; i++) {
+            if (bits.get(i)) {
                 value |= 1L << i;
             }
         }
+        if (signed && size > 1 && size < 64 && (value & (1L << (size - 1))) != 0) {
+            value |= -(1L << size); // sign-extend the two's-complement top bit
+        }
         return value;
     }