Implement underflow handling for str_decrement

Author: iluuu1994

ext/standard/string.c

@@ -1209,7 +1209,7 @@ PHP_FUNCTION(str_increment)
 		RETURN_THROWS();
 	}
 
-	zend_string *incremented = zend_string_init(ZSTR_VAL(str), ZSTR_LEN(str), /* persistant */ false);
+	zend_string *incremented = zend_string_init(ZSTR_VAL(str), ZSTR_LEN(str), /* persistent */ false);
 	size_t position = ZSTR_LEN(str)-1;
 	bool carry = false;
 
@@ -1241,7 +1241,7 @@ PHP_FUNCTION(str_increment)
 				ZSTR_VAL(tmp)[0] = ZSTR_VAL(incremented)[0];
 				break;
 		}
-		zend_string_release_ex(incremented, /* persistant */ false);
+		zend_string_release_ex(incremented, /* persistent */ false);
 		RETURN_STR(tmp);
 	}
 	RETURN_STR(incremented);
@@ -1264,8 +1264,12 @@ PHP_FUNCTION(str_decrement)
 		zend_argument_value_error(1, "must be composed only of alphanumeric ASCII characters");
 		RETURN_THROWS();
 	}
+	if (ZSTR_LEN(str) >= 1 && ZSTR_VAL(str)[0] == '0') {
+		zend_argument_value_error(1, "\"%s\" is out of decrement range", ZSTR_VAL(str));
+		RETURN_THROWS();
+	}
 
-	zend_string *decremented = zend_string_init(ZSTR_VAL(str), ZSTR_LEN(str), /* persistant */ false);
+	zend_string *decremented = zend_string_init(ZSTR_VAL(str), ZSTR_LEN(str), /* persistent */ false);
 	size_t position = ZSTR_LEN(str)-1;
 	bool carry = false;
 
@@ -1285,10 +1289,17 @@ PHP_FUNCTION(str_decrement)
 		}
 	} while (carry && position-- > 0);
 
-	if (UNEXPECTED(carry)) {
-		zend_string_release_ex(decremented, /* persistant */ false);
-		zend_argument_value_error(1, "\"%s\" is out of decrement range", ZSTR_VAL(str));
-		RETURN_THROWS();
+	if (UNEXPECTED(carry || ZSTR_VAL(decremented)[0] == '0')) {
+		if (ZSTR_LEN(decremented) == 1) {
+			zend_string_release_ex(decremented, /* persistent */ false);
+			zend_argument_value_error(1, "\"%s\" is out of decrement range", ZSTR_VAL(str));
+			RETURN_THROWS();
+		}
+		zend_string *tmp = zend_string_alloc(ZSTR_LEN(decremented) - 1, 0);
+		memcpy(ZSTR_VAL(tmp), ZSTR_VAL(decremented) + 1, ZSTR_LEN(decremented) - 1);
+		ZSTR_VAL(tmp)[ZSTR_LEN(decremented) - 1] = '\0';
+		zend_string_release_ex(decremented, /* persistent */ false);
+		RETURN_STR(tmp);
 	}
 	RETURN_STR(decremented);
 }

ext/standard/tests/strings/str_decrement_basic.phpt

@@ -13,6 +13,15 @@ $strictlyAlphaNumeric = [
     "zA",
     "Z0",
     "z0",
+    // Underflow, removing leading character
+    "Aa",
+    "aA",
+    "A0",
+    "a0",
+    "10",
+    "1A",
+    "1a",
+    "10a",
     // string interpretable as a number in scientific notation
     "5e6",
     // Interned strings
@@ -44,6 +53,22 @@ string(2) "Y9"
 string(2) "Z0"
 string(2) "y9"
 string(2) "z0"
+string(1) "z"
+string(2) "Aa"
+string(1) "Z"
+string(2) "aA"
+string(1) "9"
+string(2) "A0"
+string(1) "9"
+string(2) "a0"
+string(1) "9"
+string(2) "10"
+string(1) "Z"
+string(2) "1A"
+string(1) "z"
+string(2) "1a"
+string(2) "9z"
+string(3) "10a"
 string(3) "5e5"
 string(3) "5e6"
 string(1) "c"

ext/standard/tests/strings/str_decrement_underflow.phpt

@@ -4,14 +4,11 @@ str_decrement(): Out of Range ValueErrors for strings that cannot be decremented
 <?php
 
 $strings = [
+    "",
     "0",
     "a",
     "A",
     "00",
-    "Aa",
-    "aA",
-    "A0",
-    "a0",
     "0a",
     "0A",
 ];
@@ -26,13 +23,10 @@ foreach ($strings as $s) {
 
 ?>
 --EXPECT--
+str_decrement(): Argument #1 ($string) cannot be empty
 str_decrement(): Argument #1 ($string) "0" is out of decrement range
 str_decrement(): Argument #1 ($string) "a" is out of decrement range
 str_decrement(): Argument #1 ($string) "A" is out of decrement range
 str_decrement(): Argument #1 ($string) "00" is out of decrement range
-str_decrement(): Argument #1 ($string) "Aa" is out of decrement range
-str_decrement(): Argument #1 ($string) "aA" is out of decrement range
-str_decrement(): Argument #1 ($string) "A0" is out of decrement range
-str_decrement(): Argument #1 ($string) "a0" is out of decrement range
 str_decrement(): Argument #1 ($string) "0a" is out of decrement range
 str_decrement(): Argument #1 ($string) "0A" is out of decrement range