pshchelo

# kudos to dzaku at consolechars.wordpress.com

### MOUNT qcow2 image with lvm partitions

# ensure nbd can handle that many partitions
sudo modprobe nbd max_part=8

# present image as block device through NBD
sudo qemu-nbd --connect=/dev/nbd0 <image.qcow2>

jboner

Latency Comparison Numbers (~2012)
----------------------------------
L1 cache reference                           0.5 ns
Branch mispredict                            5   ns
L2 cache reference                           7   ns                      14x L1 cache
Mutex lock/unlock                           25   ns
Main memory reference                      100   ns                      20x L2 cache, 200x L1 cache
Compress 1K bytes with Zippy             3,000   ns        3 us
Send 1K bytes over 1 Gbps network       10,000   ns       10 us
Read 4K randomly from SSD*             150,000   ns      150 us          ~1GB/sec SSD

timtrueman

def wrap(angle):
    if angle > pi:
        angle -= (2*pi)
    if angle < -pi:
        angle += (2*pi)
    if angle < 0:
        angle += 2*pi
    return angle

def magnetometer_readings_to_tilt_compensated_heading(bx, by, bz, phi, theta):