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prep for 2.16.0.0 release with value address arithmetic restrictions

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Landon Curt Noll
2025-08-14 18:23:07 -07:00
parent db83b7383f
commit 753b101e54
8 changed files with 201 additions and 51 deletions
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help/address
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@@ -113,7 +113,7 @@ DESCRIPTION
(the case of f(0) is exceptional since 27 + 0 simply copies the 27
rather than creating a new number value). Here it is clearly more
efficient to use
efficient to use:
; A = B = C = f(2);
@@ -125,11 +125,74 @@ DESCRIPTION
and number-pointer respectively, and 0 otherwise.
The output when addresses are printed consists of a description (o_ptr,
v_ptr, s_ptr, n_ptr) followed by : and the address printed in
%p format.
v_ptr, s_ptr, n_ptr) followed by : and the address printed in %p format.
Iteration of & is not permitted; &&X causes a "non-variable operand"
scan error.
Iteration of & is not permitted; &(&X) causes a "Addressing
non-addressable type" scan error.
RESTRICTIONS ON VALUE ADDRESS ARITHMETIC
Most arithmetic operations on addresses of values are not permitted.
For example one may not perform arithmetic operations (like +, ++,
-, --, *, /, etc.) on an address of a value with a numeric value.
The reason why most arithmetic operations were removed from calc
because arithmetic on addresses of calc objects could easily cause
calc to crash. Consider this horrific expression that was allowed
in calc prior to version 2.16.0.0:
; *((&.)+1e9) /* INVALID: for calc version >= 2.16.0.0 */
Prior to calc version 2.16.0.0, some arithmetic operations on
addresses of values were permitted. Starting with calc version
2.16.0.0, arithmetic operations between an addresses and an integer
will return an error code:
; ++p; /* INVALID: will be set to E_INVALID_ADDR_OP */
; r = q - 2; /* INVALID: will be set to E_INVALID_ADDR_OP */
Adding two value addresses is NOT permitted:
; mat A[3];
; p = &A[1];
; q = &A[2];
; s = p + q; /* INVALID: will be set to E_INVALID_ADDR_OP */
Subtracting two value addresses is permitted, however there is NO
guarantee that the address of a value will remain consistent across
calc runs. Addresses of values depend on the circumstances of when
the calc values were formed. For example:
; a = 3; pa = &a;
; /* ... stuff happens ... */
; b = 5; pb = &b;
; t = pa - pb; /* permitted: value depends on circumstances */
Subtracting value addresses of components with the same compound
object, such as a matrix, is permitted. For example:
; mat M[10] = {0,1,2,3,4,5,6,7,8,9};
; i = 4; j = 5;
; p = &M[i]; q = &M[j];
; v = p - q; /* permitted: value depends on circumstances */
Comparison between two value addresses is permitted, however the
same caveats apply as to the subtracting of addresses:
; if (p < q) {
;; print "permitted: p is less than q";
;; } else if (p == q) {
;; print "permitted: p is equal to q";
;; } else {
;; print "permitted: p is greater than q";
;; }
PLEASE NOTE:
The above restrictions and caveats apply to addresses of values.
Such restrictions and caveats to NOT apply to the addresses of
octets, NOR to the addresses within strings. If isptr(x) == 2,
then x is value-pointer and the above mentioned restrictions
and caveats apply it.
EXAMPLE
Addresses for particular systems may differ from those displayed here.
@@ -160,7 +223,7 @@ LINK LIBRARY
SEE ALSO
dereference, isptr
## Copyright (C) 1999-2006,2021 Landon Curt Noll
## Copyright (C) 1999-2006,2021,2025 Landon Curt Noll
##
## Calc is open software; you can redistribute it and/or modify it under
## the terms of the version 2.1 of the GNU Lesser General Public License