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Added some more clarifications to the MACRO-10 blog post

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Jeff 2017-03-21 17:09:27 -07:00 • committed by Jeff Parsons
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_posts/2017-03-21-the-macro-10-assembler-50-years-later.md
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@ -57,10 +57,10 @@ The Debugger invokes the MACRO-10 mini-assembler whenever the argument following
As previously described in the section on [PDPjs PDP-10 Opcode Tests](/apps/pdp10/tests/opcodes/), the Debugger already
allowed you to assemble instructions directly into memory (eg, `a 100 hrli 1,111111`). This "immediate mode" feature is provided
exclusively by the Debugger; MACRO-10 mini-assembler features are not available in that mode.
exclusively by the Debugger; MACRO-10 features are not available in that mode.
However, one feature that *is* available in both the Debugger and the mini-assembler is full MACRO-10-style expression evaluation,
since they share the same expression parser. Here are some examples, using the Debugger's 'print' command:
since they share the same expression parser. Here are some examples, using the Debugger's "print" command:
>> print 27
23. 0o000027
@ -100,10 +100,26 @@ so:
>> print 5K
0o000000005000 2560.
>> print 5M
0o000005000000 1310720.
>> print 5G
0o005000000000 671088640.
>> print ^D5K
0o000000011610 5000.
>> print ^D5M
0o000023045500 5000000.
>> print ^D5G
0o045201371000 5000000000.
Binary shifting using a B suffix is also supported:
Binary shifting using a **B** suffix is also supported. Note that MACRO-10 binary shifting is a "bit" unusual by today's
standards, because the value after the **B**, *n*, is not a count but rather the desired bit position of the right-most bit of
the original value. Moreover, MACRO-10 considers bit 0 the left-most bit, and bit 35 the right-most bit. Last but not least,
*n* is always interpreted as a decimal value, regardless of the current base (radix). *n* can be converted to a shift count
by calculating (35 - n): if the count is positive, it's a left-shift, and if it's negative, it's a right-shift.
>> print 1B0
0o400000000000 -34359738368.
@ -123,8 +139,8 @@ Binary shifting using a B suffix is also supported:
>> print -1B70
0o000000000001 1.
And as the MACRO-10 ASSEMBLER PROGRAMMER'S REFERENCE MANUAL (June 1972), p. 1-17, points out, all the following expressions are
equivalent:
And as the [MACRO-10 Assembler Programmer's Reference Manual (June 1972)](http://archive.pcjs.org/pubs/dec/pdp10/tops10/Macro_Assembler_Reference_Manual-Jun72.pdf),
p. 1-17, points out, all the following expressions are equivalent:
>> print 10B32
0o000000000100 64. '@'
@ -142,7 +158,8 @@ equivalent:
0o000000000100 64. '@'
"Left arrow" shifting is also supported, although the character that the original MACRO-10 manuals referred to as a "left arrow"
is actually an underscore; later manuals refer to this as "underscore shifting":
is actually an underscore; later manuals refer to this as "underscore shifting". Underscore shifting uses straightforward shift
counts: if the count is positive, it's a left-shift, and if it's negative, it's a right-shift.
>> print 1_^D18
0o000001000000 262144.
@ -150,8 +167,12 @@ is actually an underscore; later manuals refer to this as "underscore shifting":
>> print -1_^D-18
0o000000777777 262143.
Character-based constants are also supported, in both the 7-bit ASCII and 6-bit SIXBIT formats. Use double-quotes
for 7-bit right-justified character constants and single-quotes for 6-bit right-justified character constants:
Character constants are also supported, in both the 7-bit ASCII and 6-bit SIXBIT formats. If more than 5 7-bit characters
or more than 6 6-bit characters are specified, an error will be reported, since the value cannot fit in a 36-bit word. The
character values will be stored in the same order that they are listed, but unlike values generated by MACRO-10 pseudo-ops
**ASCII**, **ASCIZ**, and **SIXBIT**, the final value will be right-justified instead of left-justified.
Use double-quotes for ASCII constants and single-quotes for SIXBIT constants:
>> print +'SIXBIT'
0o635170425164 -13255955852.
@ -159,8 +180,8 @@ for 7-bit right-justified character constants and single-quotes for 6-bit right-
>> print +"HELLO"
0o221054623117 19473311311.
NOTE: When using the PCjs debugger, the constant must be preceded by an arithmetic operator, otherwise it interprets the
quoted argument as a string. This is an idiosyncrasy of the "print" command, not the expression parser.
NOTE: When using the PCjs debugger, the constant must be preceded by an arithmetic operator (eg, '+'), otherwise it interprets
the quoted argument as a string. This is an idiosyncrasy of the "print" command, not the expression parser.
All MACRO-10 logical and arithmetic operators are supported, including: