mirror of
https://github.com/yuzu-emu/unicorn.git
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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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| .. | ||
| accel | ||
| crypto | ||
| default-configs | ||
| docs | ||
| fpu | ||
| hw | ||
| include | ||
| qapi | ||
| qobject | ||
| qom | ||
| scripts | ||
| target | ||
| tcg | ||
| util | ||
| aarch64.h | ||
| aarch64eb.h | ||
| accel.c | ||
| arm.h | ||
| armeb.h | ||
| CODING_STYLE.rst | ||
| configure | ||
| COPYING | ||
| COPYING.LIB | ||
| cpus.c | ||
| exec.c | ||
| gen_all_header.sh | ||
| glib_compat.c | ||
| header_gen.py | ||
| ioport.c | ||
| LICENSE | ||
| m68k.h | ||
| Makefile | ||
| Makefile.objs | ||
| Makefile.target | ||
| memory.c | ||
| memory_ldst.inc.c | ||
| memory_mapping.c | ||
| mips.h | ||
| mips64.h | ||
| mips64el.h | ||
| mipsel.h | ||
| powerpc.h | ||
| qemu-timer.c | ||
| riscv32.h | ||
| riscv64.h | ||
| rules.mak | ||
| sparc.h | ||
| sparc64.h | ||
| unicorn_common.h | ||
| VERSION | ||
| vl.c | ||
| vl.h | ||
| x86_64.h | ||