Emulating PS2's Emotion Engine floats. Converts the single-precision floating points of PS2 to double-precision floating points, and perform double arithmetic.
PS2's floating points are not IEEE754 compliant:-
| Exponent | Mantissa | In IEEE754 | In the PS2 |
|---|---|---|---|
| +128 | >0 | NaN | Normalized Value |
| +128 | 0 | Infinity | Normalized Value |
| -127<E<128 | Any | Normalized Value | Normalized Value |
| -127 | >0 | Subnormal Value | 0 |
| -127 | 0 | 0 | 0 |
Therefore, some large floats in the PS2 are not emulatable in x86 due to Infinity/NaN propagation. By doing a single<->double conversion, the +128 exponent is freed up (1024 is used for Inf/NaNs in doubles).
- Manually cast the float into a double (usual way of casting causes NaN propagation)
- Perform the arithmetic
- Manually cast the double back into a float (if EXP>255, return 0xFFFFFFFF; if EXP<=0, return 0x0)