FORTRAN 77 on PDP-11

Johnny Billquist wrote: Jerome Fine replies: Please define little-endian and big endian. Also, I should have explained what I meant! Specifically, it should be possible to use floating point variables as arguments to subroutines and let FORTRAN 77 take care of allocating the actual storage by doing so: 1000 FORMAT ( O25, O25 ) REAL * 8 Value1, Value2 CALL I64ADD ( Value1, Value2 ) TYPE 1000, Value1, Value2 I64ADD:: Mov R0,-(SP) Mov R1,-(SP) Mov 2(R5),R0 Mov 4(R5),R1 Add (R0)+,(R1)+ Adc (R1) Add (R0)+,(R1)+ Adc (R1)+ Add (R0)+,(R1)+ Adc (R1)+ Add (R0)+,(R1)+ Mov (SP)+,R1 Mov (SP)+,R0 Return .End This could be the code to add two 64 bit unsigned integers with the names of Value1 and Value2 which each occupy 64 bits. Of course, I could also use: INTEGER * 2 I2Val1 ( 4 ), I2Val2 ( 4 ) EQUIVALENCE ( Value1, I2Val1 ), ( Value2, I2Val2 ) but "REAL * 8" also allows the output in octal as a single 64 bit value which is quite convenient and allows me to use a single index when I need a vector of values. If I am correct, the above code assumes that the low order words/bytes are the least significant and the high order words/bytes are the most significant. Is this little-endian or big-endian? NOTE that if the most significant bit is in the most significant word and byte (as per the above MACRO-11 subroutine), then the most significant of everything is in the highest address of everything. HOWEVER, from looking at the order of bytes, words and bits in the PDP-11 manual (Chapter 10 of Microcomputer Processor Handbook), when the most significant bit is in the word with the lowest address, the most significant bit (actually the sign bit and the exponent of real floating point numbers) is in byte 1 rather than byte 0. This is not a problem per say within FORTRAN 77 as it clearly knows about these endian issues, but I found it a bit confusing at first until I realized that the bytes seemed to be interchanged within each word when the most significant bit is defined to be in word 0. On the other hand, if the most significant bit is in the byte and word with the highest address, then in FORTRAN 77 under RT-11, outputting Value1 in octal with this order of significance shows a 64 bit octal value with the most significant bit on the left and the least significant on the right. Can you please comment on the endian question? Also, am I correct about octal output of Value1? Thank you for your comments and any answers! Sincerely yours, Jerome Fine -- If you attempted to send a reply and the original e-mail address has been discontinued due a high volume of junk e-mail, then the semi-permanent e-mail address can be obtained by replacing the four characters preceding the 'at' with the four digits of the current year.