Add _global_linear_idx, a new global C-order linear index of the current element

Author: FrancescAlted

README.md

@@ -270,7 +270,7 @@ miniexpr includes a DSL (Domain-Specific Language) for writing multi-statement c
 - **Conditionals**: `where(cond, then, else)` for element-wise selection
 - **Loops**: `for var in range(limit)` iteration
 - **Control flow**: `break` and `continue` statements
-- **Index access**: Built-in `_i0`–`_i7` (position) and `_n0`–`_n7` (shape) variables
+- **Index access**: Built-in `_i0`–`_i7` (position), `_n0`–`_n7` (shape), and `_global_linear_idx` variables
 - **Function-style kernels**: `def name(args): ... return expr`
 
 ### DSL Example

doc/dsl-syntax.md

@@ -156,6 +156,7 @@ The following cannot be used as user variable/function names in DSL context:
 - `print`, `int`, `float`, `bool`, `def`, `return`
 - `_ndim`
 - `_i<d>` and `_n<d>` (reserved ND symbols)
+- `_global_linear_idx`
 
 ## ND reserved symbols
 
@@ -164,6 +165,7 @@ Supported reserved ND symbols when referenced in expressions:
 - `_i0`, `_i1`, ... (index per dimension)
 - `_n0`, `_n1`, ... (shape per dimension)
 - `_ndim`
+- `_global_linear_idx` (global C-order linear index)
 
 These are synthesized by DSL compiler/runtime when used.
 
@@ -213,4 +215,3 @@ When parser/compiler/tests change DSL behavior:
 1. Update this document in the same PR.
 2. Update or add tests in `tests/test_dsl_syntax.c` / `tests/test_nd.c`.
 3. Keep frontend validators (e.g. python-blosc2) aligned with this spec.
-

doc/dsl-usage.md

@@ -13,7 +13,7 @@ The DSL extends single expressions to full programs with:
 - **Element-wise conditionals** - Using `where(cond, true_val, false_val)`
 - **Conditional blocks** - `if/elif/else` with scalar or element-wise conditions
 - **Loop constructs** - `for`/`while` loops with `break` and `continue`
-- **Index access** - Reference element positions via `_i0`, `_i1`, etc.
+- **Index access** - Reference element positions via `_i0`, `_i1`, etc. and `_global_linear_idx`
 
 ## Basic Syntax
 
@@ -157,6 +157,7 @@ Access element positions using special variables:
 | `_i0`, `_i1`, ..., `_i7` | Current index in each dimension |
 | `_n0`, `_n1`, ..., `_n7` | Array shape in each dimension |
 | `_ndim` | Number of dimensions |
+| `_global_linear_idx` | Global C-order linear index of the current element |
 
 Example - position-dependent computation:
 ```
@@ -419,7 +420,7 @@ Rules:
 - Function/closure entries must use `ME_FUNCTION*` or `ME_CLOSURE*` in `type`.
 - The return dtype must be explicit (not `ME_AUTO`).
 - Names cannot shadow built-ins (`sin`, `sum`, etc.) or reserved identifiers
-  (`def`, `return`, `print`, `int`, `float`, `bool`, `_i0`, `_n0`, `_ndim`).
+  (`def`, `return`, `print`, `int`, `float`, `bool`, `_i0`, `_n0`, `_ndim`, `_global_linear_idx`).
 - String return types are not supported.
 
 Example (pure function):