| 1234567891011121314151617181920212223242526272829 |
- 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).
|
