From 4b12e982e6c622f7e8bb255677f712bf22c3b483 Mon Sep 17 00:00:00 2001
From: mike919192 <91038685+mike919192@users.noreply.github.com>
Date: Fri, 16 Feb 2024 04:21:25 -0500
Subject: [PATCH] In subspan function, add static checks on extents (#843)

* In subspan function, add static checks on extents

* Change to ETL_STATIC_ASSERT.  Add static assert for first and last functions

* Add static assert to pre c++11 subspan

* Change extent to Extent to better match existing code
---
 include/etl/span.h | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/include/etl/span.h b/include/etl/span.h
index 797e35e5e..2caa38975 100644
--- a/include/etl/span.h
+++ b/include/etl/span.h
@@ -42,6 +42,7 @@ SOFTWARE.
 #include "memory.h"
 #include "array.h"
 #include "byte.h"
+#include "static_assert.h"
 
 #include "private/dynamic_extent.h"
 
@@ -295,6 +296,9 @@ namespace etl
     template <size_t COUNT>
     ETL_NODISCARD ETL_CONSTEXPR etl::span<element_type, COUNT> first() const ETL_NOEXCEPT
     {
+      //if Extent is static, check that original span contains at least COUNT elements
+      ETL_STATIC_ASSERT((Extent != etl::dynamic_extent) ? COUNT <= Extent : true, "Original span does not contain COUNT elements");
+
       return etl::span<element_type, COUNT>(pbegin, pbegin + COUNT);
     }
 
@@ -312,6 +316,9 @@ namespace etl
     template <size_t COUNT>
     ETL_NODISCARD ETL_CONSTEXPR etl::span<element_type, COUNT> last() const ETL_NOEXCEPT
     {
+      //if Extent is static, check that original span contains at least COUNT elements
+      ETL_STATIC_ASSERT((Extent != etl::dynamic_extent) ? COUNT <= Extent : true, "Original span does not contain COUNT elements");
+
       return etl::span<element_type, COUNT>(pbegin + Extent - COUNT, (pbegin + Extent));
     }
 
@@ -331,6 +338,12 @@ namespace etl
     ETL_NODISCARD ETL_CONSTEXPR
     etl::span<element_type, COUNT != etl::dynamic_extent ? COUNT : Extent - OFFSET> subspan() const ETL_NOEXCEPT
     {
+      //if Extent is static, check that OFFSET is within the original span
+      ETL_STATIC_ASSERT((Extent != etl::dynamic_extent) ? OFFSET <= Extent : true, "OFFSET is not within the original span");
+
+      //if count is also static, check that OFFSET + COUNT is within the original span
+      ETL_STATIC_ASSERT((Extent != etl::dynamic_extent) && (COUNT != etl::dynamic_extent) ? COUNT <= (Extent - OFFSET) : true, "OFFSET + COUNT is not within the original span");
+      
       return (COUNT == etl::dynamic_extent) ? etl::span<element_type, COUNT != etl::dynamic_extent ? COUNT : Extent - OFFSET>(pbegin + OFFSET, (pbegin + Extent))
                                             : etl::span<element_type, COUNT != etl::dynamic_extent ? COUNT : Extent - OFFSET>(pbegin + OFFSET, pbegin + OFFSET + COUNT);
     }
@@ -341,6 +354,12 @@ namespace etl
     template <size_t OFFSET, size_t COUNT>
     etl::span<element_type, COUNT != etl::dynamic_extent ? COUNT : Extent - OFFSET> subspan() const
     {
+      //if Extent is static, check that OFFSET is within the original span
+      ETL_STATIC_ASSERT((Extent != etl::dynamic_extent) ? OFFSET <= Extent : true, "OFFSET is not within the original span");
+
+      //if count is also static, check that OFFSET + COUNT is within the original span
+      ETL_STATIC_ASSERT((Extent != etl::dynamic_extent) && (COUNT != etl::dynamic_extent) ? COUNT <= (Extent - OFFSET) : true, "OFFSET + COUNT is not within the original span");
+      
       if (COUNT == etl::dynamic_extent)
       {
         return etl::span<element_type, (COUNT != etl::dynamic_extent ? COUNT : Extent - OFFSET)>(pbegin + OFFSET, (pbegin + Extent));