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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
64 lines
2.8 KiB
C
64 lines
2.8 KiB
C
#if 0
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/*─────────────────────────────────────────────────────────────────╗
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│ To the extent possible under law, Justine Tunney has waived │
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│ all copyright and related or neighboring rights to division, │
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│ as it is written in the following disclaimers: │
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│ • http://unlicense.org/ │
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│ • http://creativecommons.org/publicdomain/zero/1.0/ │
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╚─────────────────────────────────────────────────────────────────*/
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#endif
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#include "libc/calls/calls.h"
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#include "third_party/compiler_rt/int_lib.h"
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/**
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* Divides 128-bit signed integers w/ remainder.
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*
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* @param a is numerator
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* @param b is denominator
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* @param opt_out_rem receives euclidean division remainder if not null
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* @return quotient or result of division
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* @note rounds towards zero
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*/
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COMPILER_RT_ABI ti_int __divmodti4(ti_int a, ti_int b, tu_int *opt_out_rem) {
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int k;
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tu_int r;
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ti_int sa, sb, sq, sr, x, y, q;
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k = sizeof(ti_int) * CHAR_BIT - 1;
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if (b < 0 && a == ((ti_int)1 << k)) {
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volatile int x = 0;
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x = 1 / x; // raise(SIGFPE)
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}
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sa = a >> k; // sa = a < 0 ? -1 : 0
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sb = b >> k; // sb = b < 0 ? -1 : 0
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x = (a ^ sa) - sa; // negate if sa == -1
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y = (b ^ sb) - sb; // negate if sb == -1
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sq = sa ^ sb; // sign of quotient
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sr = sa; // sign of remainder
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q = __udivmodti4(x, y, &r); // unsigned divide
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q = (q ^ sq) - sq; // fix quotient sign
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r = (r ^ sr) - sr; // fix remainder sign
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if (opt_out_rem) *opt_out_rem = r;
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return q;
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}
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/*
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Intel Kabylake i9-9900 @ 3.10GHz Client Grade
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idiv32 l: 27𝑐 9𝑛𝑠
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idiv64 l: 27𝑐 9𝑛𝑠
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divmodti4 small / small l: 42𝑐 14𝑛𝑠
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divmodti4 small / large l: 14𝑐 5𝑛𝑠
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divmodti4 large / small l: 92𝑐 30𝑛𝑠
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divmodti4 large / large l: 209𝑐 68𝑛𝑠
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Intel Kabylake i3-8100 @ 3.60GHz Client Grade
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idiv32 l: 51𝑐 14𝑛𝑠
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idiv64 l: 51𝑐 14𝑛𝑠
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divmodti4 small / small l: 83𝑐 23𝑛𝑠
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divmodti4 small / large l: 26𝑐 7𝑛𝑠
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divmodti4 large / small l: 175𝑐 48𝑛𝑠
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divmodti4 large / large l: 389𝑐 107𝑛𝑠
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*/
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