Float to XR_BIAS Conversion Rules
This section applies only to Windows 7 and later operating systems.
The following rules apply for converting float to XR_BIAS. In these rules, suppose that the starting float value is c.

If c is NaN, the result is 0; otherwise, the following rules apply. NaN stands for "not a number," which means a symbolic entity that represents a value not otherwise available in floatingpoint format.

Perform the following operation to convert from float scale to integer scale:
c = c * 510
The preceding operation might induce overflow.

Perform the following operation for bias:
c = c + 384
The preceding operation might induce overflow.

Perform one of the following operations to clamp, depending on the exponent of c:
If, post bias, the exponent of c is greater than or equal to 2 (>= 2 or c is INF), the result is 0x3ff, which is approximately equivalent to 1.2529.
If, post bias, the exponent of c is less than 0 (< 0 or c is INF), the result is 0x0, which represents approximately 0.7529.

Reinterpret the most significant 10 bits of the mantissa of c as the result.
The conversion of float to XR_BIAS is permitted tolerance of 0.6f UnitLastPlace (ULP) on the XR side. This tolerance means that after converting from float to XR, any value within 0.6f ULP of a representcapable target format value is permitted to map to that value. Note that 1 ULP of the infinitely precise result means that, for example, an implementation is permitted to truncate results to 32bit rather than perform roundtonearesteven, as that would result in an error of at most one unit in the last (least significant) place that is represented in the floatingpoint number.
The standard Direct3D version 10 requirement for inverting data also applies.