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."
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RE: Not me
by Alfman on Thu 4th Apr 2013 18:47 UTC in reply to "Not me "
Alfman
Member since:
2011-01-28

TempleOS,

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

.next:
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:
http://en.wikipedia.org/wiki/Taylor_series

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

Reply Parent Score: 2