Feature: Implement RESHAPE() in TDI

This builtin was never implemented, but the opcode was allocated and it existed in the original documentation. The similarity to numpy's reshape function means users might actually want to use this, and throwing a terse error is less than helpful.

This implements RESHAPE() with only the first two arguments of SOURCE and SHAPE. The optional arguments of PAD and ORDER described in the original documetnation are not implemented, and won't be included in the new documentation for this function.

```
TDI> reshape(1:6, [2, 3])
[[1,2], [3,4], [5,6]]

TDI> reshape(1:6, [3, 2])
[[1,2,3], [4,5,6]]

TDI> reshape(1:8, [2, 2, 2])
[[[1,2], [3,4]], [[5,6], [7,8]]]

TDI> reshape(reshape(1:8, [2, 4]), [8])
[1,2,3,4,5,6,7,8]

TDI> reshape([[1,2], [3,4]], [1, 4])
[[1], [2], [3], [4]]
```

Author: WhoBrokeTheBuild

tdishr/TdiReshape.c

@@ -28,6 +28,7 @@ OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 #include <mds_stdarg.h>
 #include <mdsdescrip.h>
 #include <tdishr.h>
+#include <mdsshr.h>
 
 #include <string.h>
 
@@ -49,7 +50,72 @@ int Tdi1Reshape(opcode_t opcode, int narg, struct descriptor *list[],
   default:
     return TdiNO_OPC;
   case OPC_RESHAPE:
-    return TdiNO_OPC;
+  {
+    uint32_t shape[MAX_DIMS] = { 0 };
+    mdsdsc_a_t dsc_shape = {
+      .length = sizeof(uint32_t),
+      .class = CLASS_A,
+      .dtype = DTYPE_LU,
+      .arsize = sizeof(shape),
+      .pointer = (char *)shape,
+    };
+
+    RETURN_IF_NOT_OK(TdiConvert((mdsdsc_a_t *)list[1], (mdsdsc_a_t *)&dsc_shape));
+
+    size_t dimct = 0;
+    size_t original_count = (arr->arsize / arr->length);
+    size_t new_count = 1;
+    for (size_t i = 0; i < MAX_DIMS; ++i) {
+      if (shape[i] == 0) {
+        break;
+      }
+
+      ++dimct;
+      new_count *= shape[i];
+    }
+
+    if (original_count != new_count) {
+      return TdiMISMATCH;
+    }
+
+    if (dimct <= arr->dimct) {
+      arr->dimct = dimct;
+      for (size_t i = 0; i < dimct; ++i) {
+        arr->m[i] = shape[i];
+      }
+    }
+    else {
+      // Need to resize the array descriptor to fit the new dims
+
+      array_coeff new_array = {
+        .length = arr->length,
+        .dtype = arr->dtype,
+        .class = arr->class,
+        .pointer = arr->pointer,
+        .scale = arr->scale,
+        .digits = arr->digits,
+        .aflags = arr->aflags,
+        .dimct = dimct,
+        .arsize = arr->arsize,
+      };
+
+      new_array.aflags.coeff = 1;
+      new_array.dimct = dimct;
+      new_array.a0 = new_array.pointer;
+      for (size_t i = 0; i < dimct; ++i) {
+        new_array.m[i] = shape[i];
+      }
+
+      mdsdsc_xd_t tmp_out_ptr = MDSDSC_XD_INITIALIZER;
+      MdsCopyDxXd((mdsdsc_t *)&new_array, &tmp_out_ptr);
+
+      // Use the new array, not the original one
+      MdsFree1Dx(out_ptr, NULL);
+      memcpy(out_ptr, &tmp_out_ptr, sizeof(mdsdsc_xd_t));
+    }
+
+    break;
+  }
   case OPC_FLATTEN:
   {
     if (arr->dimct > 1)