On Wed, Aug 5, 2009 at 10:16 PM, Don<nos...@nospam.com> wrote: > Lars T. Kyllingstad wrote: >> >> Lars T. Kyllingstad wrote: >>> >>> Here's a puzzle for you floating-point wizards out there. I have to >>> translate the following snippet of FORTRAN code to D: >>> >>> REAL B,Q,T >>> C ------------------------------ >>> C |*** COMPUTE MACHINE BASE ***| >>> C ------------------------------ >>> T = 1. >>> 10 T = T + T >>> IF ( (1.+T)-T .EQ. 1. ) GOTO 10 >>> B = 0. >>> 20 B = B + 1 >>> IF ( T+B .EQ. T ) GOTO 20 >>> IF ( T+2.*B .GT. T+B ) GOTO 30 >>> B = B + B >>> 30 Q = ALOG(B) >>> Q = .5/Q >>> >>> Of course I could just do a direct translation, but I have a hunch that >>> T, B, and Q can be expressed in terms of real.epsilon, real.min and so >>> forth. I have no idea how, though. Any ideas? >>> >>> (I am especially puzzled by the line after l.20. How can this test ever >>> be true? Is the fact that the 1 in l.20 is an integer literal significant?) >>> >>> -Lars >> >> >> I finally solved the puzzle by digging through ancient scientific papers, >> as well as some old FORTRAN and ALGOL code, and the solution turned out to >> be an interesting piece of computer history trivia. >> >> After the above code has finished, the variable B contains the radix of >> the computer's numerical system. >> >> Perhaps the comment should have tipped me off, but I had no idea that >> computers had ever been anything but binary. But apparently, back in the 50s >> and 60s there were computers that used the decimal and hexadecimal systems >> as well. Instead of just power on/off, they had 10 or 16 separate voltage >> levels to differentiate between bit values. > > Not quite. They just used exponents which were powers of 10 or 16, rather > than 2. BTW, T == 1/real.epsilon. I don't know what ALOG does, so I've no > idea what Q is.
Apparently ALOG is just an old name for LOG. At least that's what Google tells me.
