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John Calsbeek Nexuapex

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Nexuapex / absl_flat_hash_map_latency.txt
Created October 1, 2018 01:42
// Abseil absl::flat_hash_map
// Analysis of the critical path for perfectly predicted load hit.
// https://godbolt.org/z/P_ksaa
//
// x86_64
// Instruction latencies have been entirely ignored.
# rdi = desired key
mov rax, qword ptr [rip + kHashSeed] # [a00] rax = per-process seed (with entropy)
add rax, rdi # [a01] rax = hash so far
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Nexuapex / bit_cast.h
Created April 1, 2018 19:32
Minimal-dependencies implementation of bit_cast.
#include <string.h>
#if defined(__has_attribute)
#if __has_attribute(always_inline)
#define ALWAYS_INLINE __attribute__((always_inline))
#endif
#endif
#if defined(_MSC_VER)
// To reduce debug build overhead:
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Nexuapex / workerpool.py
Created January 8, 2015 03:15
Simple Python MPMC queue and thread pool.
from __future__ import absolute_import
import sys
import threading
import collections
class WorkerPool(object):
"""A thread pool that processes items from an unbounded work queue, for
simple multi-producer, multi-consumer processes.
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Nexuapex / resource_table.cc
Created April 26, 2016 06:06
Sketch of a few ways to store 8 or 16 elements indexed by a packed byte array.
#include <xmmintrin.h>
#include <stdint.h>
struct ResourceTable8
{
uint64_t type_bits_;
uintptr_t elements_[8];
inline uint64_t mask_for_type(uint8_t type)
{
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Nexuapex / msvcrt_heap_exc.cc
Last active December 24, 2015 01:29
There's this handy flag on Win32 heap objects called HEAP_GENERATE_EXCEPTIONS, which causes the heap manager to raise a structured exception instead of returning null on a failed allocation. But the C runtime creates its heap behind the scenes and doesn't allow you access to it, and you can't add this flag after creation anyway. Unless you are t…
#include <malloc.h>
#include <windows.h>
static HANDLE FindCrtHeap()
{
// Pick a block that we know is in the CRT heap.
//
_HEAPINFO crtEntry = {};
if (_HEAPOK != _heapwalk(&crtEntry))
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Nexuapex / kahan3.c
Created August 23, 2012 05:12
Kahan summation (3-way)
float sum(float x0, float x1, float x2)
{
float accum = x0 + x1;
float excess = (accum - x0) - x1;
float addend = x2 - excess;
return accum + addend;
}
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Nexuapex / dump.lua
Created June 17, 2012 02:50
Dumping a description of a Lua value
local dump_table_threshold = 3
local dump_indent = (" "):rep(4)
local dumptable = {
["nil"] = tostring,
["number"] = tostring,
["string"] = function(value) return "\"" .. value .. "\"" end,
["boolean"] = tostring,
["table"] = function(value, depth, markers)
if markers[value] then
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Nexuapex / reinterpret_f32_i32_sse.cc
Created February 18, 2012 05:10
Reinterpreting int ⇔ float with SSE
#include <xmmintrin.h>
inline int as_int_bitwise(float a)
{
return _mm_cvtsi128_si32(_mm_set_ss(a));
}
inline float as_float_bitwise(int a)
{
return _mm_cvtss_f32(_mm_cvtsi32_si128(a));
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Nexuapex / icosahedron.cc
Created February 7, 2012 10:33
Icosahedron
static GLfloat const minor = 0.5257311f;
static GLfloat const major = 0.8506508f;
float const icosahedron_position[12][3] = {
{0.f, +minor, +major},
{0.f, +minor, -major},
{0.f, -minor, +major},
{0.f, -minor, -major},
{+major, 0.f, +minor},
{+major, 0.f, -minor},
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Nexuapex / 7segment.c
Created October 29, 2011 04:39
7-segment display in 50 lines of C99.
#include <stdio.h>
int const schematic[7][7] = {
{0,1,1,1,1,0,0},
{2,0,0,0,0,3,0},
{2,0,0,0,0,3,0},
{0,4,4,4,4,0,0},
{5,0,0,0,0,6,0},
{5,0,0,0,0,6,0},
{0,7,7,7,7,0,0},