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2aee4714ab
The x87 f2xm1 emulation is currently based around conversion to double. This is inherently unsuitable for a good emulation of any floatx80 operation, even before considering that it is a particularly naive implementation using double (computing with pow and then subtracting 1 rather than attempting a better emulation using expm1). Reimplement using the soft-float operations, including additions and multiplications with higher precision where appropriate to limit accumulation of errors. I considered reusing some of the m68k code for transcendental operations, but the instructions don't generally correspond exactly to x87 operations (for example, m68k has 2^x and e^x - 1, but not 2^x - 1); to avoid possible accumulation of errors from applying multiple such operations each rounding to floatx80 precision, I wrote a direct implementation of 2^x - 1 instead. It would be possible in principle to make the implementation more efficient by doing the intermediate operations directly with significands, signs and exponents and not packing / unpacking floatx80 format for each operation, but that would make it significantly more complicated and it's not clear that's worthwhile; the m68k emulation doesn't try to do that. A test is included with many randomly generated inputs. The assumption of the test is that the result in round-to-nearest mode should always be one of the two closest floating-point numbers to the mathematical value of 2^x - 1; the implementation aims to do somewhat better than that (about 70 correct bits before rounding). I haven't investigated how accurate hardware is. Backports commit eca30647fc078f4d9ed1b455bd67960f99dbeb7a from qemu |
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| .. | ||
| arch_memory_mapping.c | ||
| bpt_helper.c | ||
| cc_helper.c | ||
| cc_helper_template.h | ||
| cpu-param.h | ||
| cpu-qom.h | ||
| cpu.c | ||
| cpu.h | ||
| excp_helper.c | ||
| fpu_helper.c | ||
| helper.c | ||
| helper.h | ||
| int_helper.c | ||
| Makefile.objs | ||
| mem_helper.c | ||
| misc_helper.c | ||
| mpx_helper.c | ||
| ops_sse.h | ||
| ops_sse_header.h | ||
| seg_helper.c | ||
| shift_helper_template.h | ||
| smm_helper.c | ||
| svm.h | ||
| svm_helper.c | ||
| topology.h | ||
| translate.c | ||
| unicorn.c | ||
| unicorn.h | ||