SFLOAT-Type Data Type
This data type is a floating point number type specified in the IEEE 11073-20601 standard and is a shortened version of the FLOAT-Type data type.[1] It is stored and interpreted differently compared to the often seen implemented floating point number according to the IEEE 754 standard. The SFLOAT-Type defined in standard IEEE 11073-20601 focuses on health informatics – personal health device communication and the category application profile – optimized exchange protocol.[2] Medical devices like glucose meters, blood pressure meters, blood oxygen saturation devices, etc. implement the optimized exchange protocol.[3] Mobile devices implement wireless communication via Bluetooth in order to secure the transport to gateways.[4]
Data Type
The Bluetooth SIG offers a public white paper which describes the SFLOAT-Type as a 16-bit value containing a 4-bit exponent to base 10, followed by a 12-bit mantissa.[1]
Special values
The Bluetooth SIG white paper also explains special values, which can be used for edge cases:[1]
| Abbreviation | Description | Exponent | Mantissa | Hex Value | Binary Value |
|---|---|---|---|---|---|
| NaN | Not a Number | 0 | +(211-1) | 0x07FF
|
0000 0111 1111 1111
|
| NRes | Not at this Resolution | 0 | -(211) | 0x0800
|
0000 1000 0000 0000
|
| +INFINITY | 0 | +(211-2) | 0x07FE
|
0000 0111 1111 1110
| |
| -INFINITY | 0 | -(211-2) | 0x0802
|
0000 1000 0000 0010
| |
| Reserved for future use | 0 | -(211-1) | 0x0801
|
0000 1000 0000 0001
|
Examples
Imagine a blood pressure measurement of 114 mmHg (precision is 1 mmHg). The final value as SFLOAT-Type representation is 0x0072.[1]
In the binary representation below, the exponent can be seen as 0 (0x0) in the first 4 bits and the mantissa can be seen as 114 (0x072) in the following 12 bits.
For another example we look at a blood glucose measurement of 0.00118 kg/l (precision is 0.00001 kg/l) which has a SFLOAT-Type representation of 0xB076. The code below shows how the value can be derived from its SFLOAT-Type representation.[5]
sfloat_value = 0xB076
mantissa = sfloat_value & 0x0FFF
if (mantissa >= 0x0800):
mantissa = -((0x0FFF + 1) - mantissa)
exponent = sfloat_value >> 12
if (exponent >= 0x0008):
exponent = -((0x000F + 1) - exponent)
magnitude = pow(10.0, exponent)
measurement = (mantissa * magnitude)
References
- ↑ 1.0 1.1 1.2 1.3 "Personal Health Devices Transcoding" (PDF). Medical Devices Working Group. Retrieved 14 June 2022.
- ↑ "IEEE Standards Association".
- ↑ https://www.bluetooth.com/wp-content/uploads/2019/03/HDP-Implementation_WP_V10.pdf [bare URL PDF]
- ↑ https://www.pchalliance.org/sites/pchalliance/files/Fundamentals_Medical-Grade_Data_Exchange_Dec2021.pdf [bare URL PDF]
- ↑ https://openconnectivity.org/specs/OCF_Resource_to_BLE_Mapping_Specification_v2.1.0.pdf [bare URL PDF]
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