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f4f4caab0e
I wanted a tiny scriptable meltdown proof way to run userspace programs and visualize how program execution impacts memory. It helps to explain how things like Actually Portable Executable works. It can show you how the GCC generated code is going about manipulating matrices and more. I didn't feel fully comfortable with Qemu and Bochs because I'm not smart enough to understand them. I wanted something like gVisor but with much stronger levels of assurances. I wanted a single binary that'll run, on all major operating systems with an embedded GPL barrier ZIP filesystem that is tiny enough to transpile to JavaScript and run in browsers too. https://justine.storage.googleapis.com/emulator625.mp4
28 lines
1.2 KiB
C
28 lines
1.2 KiB
C
#ifndef COSMOPOLITAN_LIBC_NEXGEN32E_BSR_H_
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#define COSMOPOLITAN_LIBC_NEXGEN32E_BSR_H_
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#if !(__ASSEMBLER__ + __LINKER__ + 0)
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COSMOPOLITAN_C_START_
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/*
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* BIT SCANNING 101
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* ctz(𝑥) 31^clz(𝑥) clz(𝑥)
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* uint32 𝑥 bsf(𝑥) tzcnt(𝑥) ffs(𝑥) bsr(𝑥) lzcnt(𝑥)
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* 0x00000000 wut 32 0 wut 32
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* 0x00000001 0 0 1 0 31
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* 0x80000001 0 0 1 31 0
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* 0x80000000 31 31 32 31 0
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* 0x00000010 4 4 5 4 27
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* 0x08000010 4 4 5 27 4
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* 0x08000000 27 27 28 27 4
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* 0xffffffff 0 0 1 31 0
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*/
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#define bsr(u) ((sizeof(unsigned) * 8 - 1) ^ __builtin_clz(u))
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#define bsrl(u) ((sizeof(unsigned long) * 8 - 1) ^ __builtin_clzl(u))
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#define bsrll(u) ((sizeof(unsigned long long) * 8 - 1) ^ __builtin_clzll(u))
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unsigned bsrmax(uintmax_t);
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COSMOPOLITAN_C_END_
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#endif /* !(__ASSEMBLER__ + __LINKER__ + 0) */
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#endif /* COSMOPOLITAN_LIBC_NEXGEN32E_BSR_H_ */
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