LBOUND / UBOUND

Syntax

Syntax: LBOUND(array) | UBOUND(array)
Source: pb_cg_emit_bound_builtin (pb_codegen.c:4176)

Description

LBOUND returns the lowest valid index (lower bound) of an array. UBOUND returns the highest valid index (upper bound). These are essential for writing loops that iterate over arrays without hard-coding index ranges.

For fixed arrays the bounds are compile-time constants. The compiler emits an immediate MOV.
For dynamic arrays (REDIM) the bounds are stored in the array descriptor at runtime and are loaded from the stack frame.

Parameters

Parameter	Description
`array`	Any array variable (fixed or dynamic)

Example

LOCAL a(1 TO 10) AS LONG
LOCAL i AS LONG
FOR i = LBOUND(a) TO UBOUND(a)
    a(i) = i * 2
NEXT i

REDIM d(5 TO 15) AS LONG
LOCAL lo, hi AS LONG
lo = LBOUND(d)          ' lo = 5
hi = UBOUND(d)          ' hi = 15

Dynamic Array (REDIM)

; LBOUND: load from descriptor in stack frame
mov    rax, [rbp - lower_offset]         ; runtime lower bound

; UBOUND: load from descriptor
mov    rax, [rbp - upper_offset]         ; runtime upper bound

Fixed Array

; LBOUND: compile-time constant
mov    rax, <constant_lower>             ; e.g., 0 or 1

; UBOUND: compile-time constant
mov    rax, <constant_upper>             ; e.g., 10

Array Descriptor Layout (per array in stack frame)

; Dynamic array descriptor:
[rbp - ptr_offset]      ; pointer to heap data (from malloc)
[rbp - lower_offset]    ; lower bound (from REDIM)
[rbp - upper_offset]    ; upper bound (from REDIM)
[rbp - count_offset]    ; element count
[rbp - capacity_offset] ; allocated capacity
[rbp - stride_offset]   ; bytes per element

; Fixed array: just the data inline
[rbp - base + i*stride]  ; elements laid out contiguously