replace sbs_cut with more powerful sbs_substr

src/report.c

@@ -1550,7 +1550,7 @@ void pump_paragraph(sbstring *sbp, stream *out, size_t maxlen, bool isfinal)
                 return;
             }
             else if (next > begin + maxlen) {
-                size_t len = pos - begin;
+                ptrdiff_t len = pos - begin;
                 swrite(begin, 1, len, out);
                 newline(out);
 
@@ -1558,8 +1558,8 @@ void pump_paragraph(sbstring *sbp, stream *out, size_t maxlen, bool isfinal)
                     ++pos;
                     ++len;
                 }
-                assert(len <= INT_MAX);
-                sbs_cut(sbp, (int)len);
+                assert(len <= SIZE_MAX);
+                sbs_substr(sbp, len, SIZE_MAX);
                 break;
             }
             pos = next;

src/util/strings.c

@@ -298,19 +298,24 @@ void sbs_strcpy(struct sbstring *sbs, const char *str)
     assert(sbs->begin + sbs->size >= sbs->end);
 }
 
-void sbs_cut(sbstring *sbs, int bytes)
+void sbs_substr(sbstring *sbs, ptrdiff_t pos, size_t len)
 {
-    if (bytes > 0) {
-        size_t len = sbs_length(sbs) - bytes;
-        memmove(sbs->begin, sbs->begin + bytes, len + 1);
-        sbs->end = sbs->begin + len;
+    if (pos > sbs->end - sbs->begin) {
+        /* starting past end of string, do nothing */
+        sbs->end = sbs->begin;
     }
-    else if (bytes < 0) {
-        size_t len = sbs_length(sbs) + bytes;
+    if (pos >= 0) {
+        size_t sz = sbs->end - (sbs->begin + pos);
+        if (len > sz) len = sz;
+        if (len - pos > 0) {
+            memmove(sbs->begin, sbs->begin + pos, len);
+        }
+        else {
+            memcpy(sbs->begin, sbs->begin + pos, len);
+        }
         sbs->end = sbs->begin + len;
+        sbs->end[0] = '\0';
     }
-    assert(sbs->begin + sbs->size >= sbs->end);
-    assert(sbs->end[0] == '\0');
 }
 
 size_t sbs_length(const struct sbstring *sbs)

src/util/strings.h

@@ -52,7 +52,7 @@ extern "C" {
     void sbs_strcat(struct sbstring *sbs, const char *str);
     void sbs_strncat(struct sbstring *sbs, const char *str, size_t size);
     void sbs_strcpy(struct sbstring *sbs, const char *str);
-    void sbs_cut(struct sbstring *sbp, int bytes);
+    void sbs_substr(struct sbstring *sbp, ptrdiff_t pos, size_t len);
     size_t sbs_length(const struct sbstring *sbs);
 
     /* benchmark for units:

src/util/strings.test.c

@@ -191,6 +191,45 @@ static void test_sbs_strcat(CuTest * tc)
     CuAssertStrEquals(tc, "1234123", sbs.begin);
 }
 
+static void test_sbs_substr(CuTest * tc)
+{
+    char buffer[10];
+    sbstring sbs;
+
+    buffer[9] = 'A';
+    sbs_init(&sbs, buffer, sizeof(buffer));
+    sbs_strcpy(&sbs, "12345678");
+    CuAssertStrEquals(tc, "12345678", buffer);
+    sbs_substr(&sbs, 0, 4);
+    CuAssertStrEquals(tc, "1234", buffer);
+    CuAssertIntEquals(tc, 4, (int)sbs_length(&sbs));
+
+    sbs_strcpy(&sbs, "12345678");
+    CuAssertStrEquals(tc, "12345678", buffer);
+    sbs_substr(&sbs, 4, 4);
+    CuAssertStrEquals(tc, "5678", buffer);
+    CuAssertIntEquals(tc, 4, (int)sbs_length(&sbs));
+
+    sbs_strcpy(&sbs, "12345678");
+    CuAssertStrEquals(tc, "12345678", buffer);
+    sbs_substr(&sbs, 2, 4);
+    CuAssertStrEquals(tc, "3456", buffer);
+    CuAssertIntEquals(tc, 4, (int)sbs_length(&sbs));
+
+    sbs_strcpy(&sbs, "12345678");
+    CuAssertStrEquals(tc, "12345678", buffer);
+    sbs_substr(&sbs, 4, 4);
+    CuAssertStrEquals(tc, "5678", buffer);
+    CuAssertIntEquals(tc, 4, (int)sbs_length(&sbs));
+
+    sbs_strcpy(&sbs, "12345678");
+    CuAssertStrEquals(tc, "12345678", buffer);
+    sbs_substr(&sbs, 4, 8);
+    CuAssertStrEquals(tc, "5678", buffer);
+    CuAssertIntEquals(tc, 4, (int)sbs_length(&sbs));
+    CuAssertIntEquals(tc, 'A', buffer[9]);
+}
+
 CuSuite *get_strings_suite(void)
 {
     CuSuite *suite = CuSuiteNew();
@@ -205,5 +244,6 @@ CuSuite *get_strings_suite(void)
     SUITE_ADD_TEST(suite, test_str_itoa);
     SUITE_ADD_TEST(suite, test_sbstring);
     SUITE_ADD_TEST(suite, test_sbs_strcat);
+    SUITE_ADD_TEST(suite, test_sbs_substr);
     return suite;
 }