How to convert IEEE-11073 16-bit SFLOAT to simple float in Java?

Question

The title speaks for itself: How to convert IEEE-11073 16-bit SFLOAT to simple float in Java?

Answer 1

This 11073 library has C code that does that:

https://github.com/signove/antidote/blob/master/src/util/bytelib.c

Should not be difficult to convert to Java.

double read_sfloat(ByteStreamReader *stream, int *error)
{
    intu16 int_data = read_intu16(stream, error);
    if (*error)
        return 0;

    intu16 mantissa = int_data & 0x0FFF;
    int8 expoent = int_data >> 12;

    if (expoent >= 0x0008) {
        expoent = -((0x000F + 1) - expoent);
    }

    float output = 0;

    if (mantissa >= FIRST_S_RESERVED_VALUE && mantissa
        <= MDER_S_NEGATIVE_INFINITY) {
        output = reserved_float_values[mantissa
                           - FIRST_S_RESERVED_VALUE];
    } else {
        if (mantissa >= 0x0800) {
            mantissa = -((0x0FFF + 1) - mantissa);
        }
        double magnitude = pow(10.0f, expoent);
        output = (mantissa * magnitude);
    }

    return output;
}

The boilerplate code:

typedef enum {
    MDER_S_POSITIVE_INFINITY = 0x07FE,
    MDER_S_NaN = 0x07FF,
    MDER_S_NRes = 0x0800,
    MDER_S_RESERVED_VALUE = 0x0801,
    MDER_S_NEGATIVE_INFINITY = 0x0802
} ReservedSFloatValues;

static const intu32 FIRST_S_RESERVED_VALUE = MDER_S_POSITIVE_INFINITY;

intu16 read_intu16(ByteStreamReader *stream, int *error)
{
    intu16 ret = 0;

    if (stream && stream->unread_bytes > 1) {
        ret = ntohs(*((uint16_t *) stream->buffer_cur));

        stream->buffer_cur += 2;
        stream->unread_bytes -= 2;
    } else {
        if (error) {
            *error = 1;
        }

        ERROR("read_intu16");
    }

    return ret;
}

Answer 2

IEEE-11073 is not in public domain but you can find sufficient information in Bluetooth personal health profiles. Google up with full spec# 11073-2060. Following is copy paste from a bluetooth personal health transcoding paper:

The following information is defined in ISO/IEEE Std. 11073-2060™1-2008 [1].

The SFLOAT-Type data type is defined to represent numeric values that are not integer in type. The SFLOAT-Type is defined as a 16-bit value with 12-bit mantissa and 4-bit exponent. See Annex F.8 of [1] for a thorough definition of the SFLOAT-Type. This data type is defined as follows:

	Exponent	Mantissa
Size	4 bit	12 bit

16-bit float type; the integer type is a placeholder only

SFLOAT-Type ::= INT-U16

The 16–bit value contains a 4-bit exponent to base 10, followed by a 12-bit mantissa. Each is in twos-complement form.

Special values are assigned to express the following:

• NaN [exponent 0, mantissa +(2^11 –1) → 0x07FF]
• NRes [exponent 0, mantissa > –(2^11) → 0x0800]

• INFINITY [exponent 0, mantissa +(2^11 –2) → 0x07FE] – INFINITY [exponent 0, mantissa –(2^11 –2) → 0x0802]

• Reserved for future use [exponent 0, mantissa –(2^11 –1) → 0x0801]