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Diffstat (limited to 'Documentation/arm/nwfpe/NOTES')
| -rw-r--r-- | Documentation/arm/nwfpe/NOTES | 29 |
1 files changed, 0 insertions, 29 deletions
diff --git a/Documentation/arm/nwfpe/NOTES b/Documentation/arm/nwfpe/NOTES deleted file mode 100644 index 40577b5a49d3..000000000000 --- a/Documentation/arm/nwfpe/NOTES +++ /dev/null @@ -1,29 +0,0 @@ -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). |