Linked by Thom Holwerda on Wed 3rd Apr 2013 21:45 UTC
Apple "Thanks to 35-year-old documents that have recently surfaced after three-plus decades in storage, we now know exactly how Apple navigated around that obstacle to create the company's first disk operating system. In more than a literal sense, it is also the untold story of how Apple booted up. From contracts - signed by both Wozniak and Jobs - to design specs to page after page of schematics and code, CNET had a chance to examine this document trove, housed at the DigiBarn computer museum in California's Santa Cruz Mountains, which shed important new light on those formative years at Apple."
Permalink for comment 557640
To read all comments associated with this story, please click here.
RE: Not me
by Alfman on Thu 4th Apr 2013 18:47 UTC in reply to "Not me "
Member since:


Note that you can (and should) reply to specific posts instead of starting a new comment thread each time.

"For everybody who does not know the joys of MUL and DIV without CPU instructions, have a look:"

Anyways, I noticed your mul uses a conditional jump inside the loop that I think could be avoided by doing bit manipulations. Here's some untested code that eliminates the inner jump. Who knows if it'd make a difference in execution time on x86, where this is obviously just for fun. But it might make a difference on the earlier processors where branches were expensive?

mov rax, A ; input
mov rbx, B ; input
mov rcx, 64 ; loop counter
xor rdx, rdx ; output

mov rsi, rax
and rsi, 0x0001 ; isolate lsb = 0 , 1
neg rsi ; = 0 , 0xffff...
and rsi, rbx ; = 0 , rbx
add rdx, rsi ; add in
shr rax, 1
shl rbx, 1
loop .next

; rdx = A * B

"Taylor is slow to converge, so I've heard. I'm sure there was a standard way to do trig by 1975."

It's very easy to recognize on a plot after even just 3 taylor terms, each additional 2 terms represents another full sine cycle, it takes shape pretty quick around the origin, but I hadn't measured the actual accuracy.

It's not very good, but wikipedia does have a picture:

Anyways I was just curious if you knew what algorithms the early computers actually used, not that it matters much.

Reply Parent Score: 2