Merge #19027

19027: sys/fmt: optimize scn_u32_dec scn_u32_hex r=benpicco a=kfessel ### Contribution description Improves the compilation result for `scn_u32_dec` `scn_u32_hex` especially on `cortex-m` reducing either stack usage and or code size. This makes use of unsigned int overflow (slightly less better without doing that `hexn`). See godbolt (original versions got an `o` attached, modified versions got `k`s) all functions are marked `_S_` defined to `static` by assigning the global at end the compiled function can be changed (`deco deck hexo hexk hexkk hexn`) this PR is `hexkk` and `deck` ### Testing procedure run unit-test/test-fmt ``` <RIOT>/tests/unittests$ make tests-fmt <RIOT>/tests/unittests$ make term ``` ### Issues/PRs references [godbolt](https://godbolt.org/z/MzT1zh4q1) Co-authored-by: Karl Fessel <karl.fessel@ovgu.de>
RIOT-OS · Feb 17, 2023 · 8c2a4b4 · 8c2a4b4
2 parents b1be519 + 18a783d
commit 8c2a4b4
Showing 1 changed file with 19 additions and 18 deletions.
diff --git a/sys/fmt/fmt.c b/sys/fmt/fmt.c
@@ -471,14 +471,13 @@ uint32_t scn_u32_dec(const char *str, size_t n)
     uint32_t res = 0;
 
     while (n--) {
-        char c = *str++;
-        if (!fmt_is_digit(c)) {
+        unsigned c = *str++;
+        unsigned d = c - (unsigned)'0';
+        if ( !( '0'<= c && c <= '9') ) {
             break;
         }
-        else {
-            res *= 10;
-            res += (c - '0');
-        }
+        res *= 10U;
+        res += d;
     }
     return res;
 }
@@ -488,21 +487,23 @@ uint32_t scn_u32_hex(const char *str, size_t n)
     uint32_t res = 0;
 
     while (n--) {
-        char c = *str++;
-        if (!fmt_is_digit(c)) {
-            if (fmt_is_upper(c)) {
-                c = _to_lower(c);
-            }
-            if (c == '\0' || c > 'f') {
-                break;
-            }
-            res <<= 4;
-            res |= c - 'a' + 0xa;
+        unsigned c = *str++;
+        unsigned d;
+        if (('0'<= c) && (c <= '9')){
+            d = c - (unsigned)'0';
+        }
+        else if (('A' <= c) && (c <= 'F')) {
+            d = c - (unsigned)'A' + 0xaU;
+        }
+        else if (('a' <= c) && (c <= 'f')) {
+            d = c - (unsigned)'a' + 0xaU;
         }
         else {
-            res <<= 4;
-            res |= c - '0';
+            break;
         }
+        res <<= 4U;
+        res |= d;
+
     }
     return res;
 }