| There seems to be a problem with exp(double) and our emulator. I haven't |
| been able to track it down yet. This does not occur with the emulator |
| supplied by Russell King. |
| |
| I also found one oddity in the emulator. I don't think it is serious but |
| will point it out. The ARM calling conventions require floating point |
| registers f4-f7 to be preserved over a function call. The compiler quite |
| often uses an stfe instruction to save f4 on the stack upon entry to a |
| function, and an ldfe instruction to restore it before returning. |
| |
| I was looking at some code, that calculated a double result, stored it in f4 |
| then made a function call. Upon return from the function call the number in |
| f4 had been converted to an extended value in the emulator. |
| |
| This is a side effect of the stfe instruction. The double in f4 had to be |
| converted to extended, then stored. If an lfm/sfm combination had been used, |
| then no conversion would occur. This has performance considerations. The |
| result from the function call and f4 were used in a multiplication. If the |
| emulator sees a multiply of a double and extended, it promotes the double to |
| extended, then does the multiply in extended precision. |
| |
| This code will cause this problem: |
| |
| double x, y, z; |
| z = log(x)/log(y); |
| |
| The result of log(x) (a double) will be calculated, returned in f0, then |
| moved to f4 to preserve it over the log(y) call. The division will be done |
| in extended precision, due to the stfe instruction used to save f4 in log(y). |
