On Wed, Aug 5, 2009 at 8:07 AM, Lars T. Kyllingstad<pub...@kyllingen.nospamnet> 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. > > I guess I can just drop this part from my code, then. ;)
Very interesting! Thanks for sharing that. But I'm not so sure about the 16 separate voltage levels part. I think they were probably binary underneath. Like the BCD (Binary Coded Decimal) system. --bb
