table.fill: Bounds check before mutating the table (#106)

Fixes #105

Author: fitzgen

document/core/exec/instructions.rst

@@ -651,42 +651,49 @@ Table Instructions
 
 11. Pop the value :math:`\I32.\CONST~i` from the stack.
 
-12. If :math:`n` is :math:`0`, then:
+12. If :math:`i + n` is larger than the length of :math:`\X{tab}.\TIELEM`, then:
 
-    a. If :math:`i` is larger than the length of :math:`\X{tab}.\TIELEM`, then:
+    a. Trap.
 
-       i. Trap.
+12. If :math:`n` is :math:`0`, then:
 
-12. Else:
+    a. Return.
 
-    a. Push the value :math:`\I32.CONST~i` to the stack.
+13. Push the value :math:`\I32.CONST~i` to the stack.
 
-    b. Push the value :math:`\val` to the stack.
+14. Push the value :math:`\val` to the stack.
 
-    c. Execute the instruction :math:`\TABLESET~x`.
+15. Execute the instruction :math:`\TABLESET~x`.
 
-    d. Push the value :math:`\I32.CONST~(i+1)` to the stack.
+16. Push the value :math:`\I32.CONST~(i+1)` to the stack.
 
-    e. Push the value :math:`\val` to the stack.
+17. Push the value :math:`\val` to the stack.
 
-    f. Push the value :math:`\I32.CONST~(n-1)` to the stack.
+18. Push the value :math:`\I32.CONST~(n-1)` to the stack.
 
-    c. Execute the instruction :math:`\TABLEFILL~x`.
+19. Execute the instruction :math:`\TABLEFILL~x`.
 
 .. math::
    \begin{array}{l}
-   \begin{array}{lcl@{\qquad}l}
-   S; F; (\I32.\CONST~i)~\val~(\I32.\CONST~(n+1))~(\TABLEFILL~x) &\stepto& S'; F; (\I32.\CONST~i)~\val~(\TABLESET~x)~(\I32.\CONST~(i+1))~\val~(\I32.\CONST~n)~(\TABLEFILL~x)
-   \end{array} \\
-   \begin{array}{lcl@{\qquad}l}
-   S; F; (\I32.\CONST~i)~\val~(\I32.\CONST~0)~(\TABLEFILL~x) &\stepto& S'; F; \epsilon
-   \end{array}
-   \\ \qquad
-     (\iff i \leq |\STABLES[F.\AMODULE.\MITABLES[x]]|) \\
-   \begin{array}{lcl@{\qquad}l}
-   S; F; (\I32.\CONST~i)~\val~(\I32.\CONST~0)~(\TABLEFILL~x) &\stepto& S; F; \TRAP
-   \end{array}
-   \\ \qquad
+   S; F; (\I32.\CONST~i)~\val~(\I32.\CONST~n)~(\TABLEFILL~x)
+     \quad\stepto\quad S; F; \TRAP
+     \\ \qquad
+     \begin{array}[t]{@{}r@{~}l@{}}
+     (\iff & i + n > |S.\STABLES[F.\AMODULE.\MITABLES[x]].\TIELEM|) \\
+     \end{array}
+   \\[1ex]
+   S; F; (\I32.\CONST~i)~\val~(\I32.\CONST~0)~(\TABLEFILL~x)
+     \quad\stepto\quad S; F; \epsilon
+     \\ \qquad
+     (\otherwise)
+   \\[1ex]
+   S; F; (\I32.\CONST~i)~\val~(\I32.\CONST~n+1)~(\TABLEFILL~x)
+     \quad\stepto\quad S; F;
+       \begin{array}[t]{@{}l@{}}
+       (\I32.\CONST~i)~\val~(\TABLESET~x) \\
+       (\I32.\CONST~i+1)~\val~(\I32.\CONST~n)~(\TABLEFILL~x) \\
+       \end{array}
+     \\ \qquad
      (\otherwise) \\
    \end{array}