I’m rich in flash space in this application so I used a spreadsheet to build me a lookup table of tenths of a degree, along the lines of:
static const int16_t temp_lookup[4096] = {
-457,
-457,
-456,
...
1713,
1714,
1715,
1715
};
The exact values in the table are unique to my front-end so not relevant to you, but to build it I just used the standard pt1000 formula and you can find that all over the web, one example here.