SAS reader: fix value labels for negative numbers

Author: evanmiller

src/sas/readstat_sas7bcat_read.c

@@ -107,7 +107,12 @@ static readstat_error_t sas7bcat_parse_value_labels(const char *value_start, siz
                 sas_assign_tag(&value, (val >> 40));
             } else {
                 memcpy(&dval, &val, 8);
-                dval *= -1.0;
+                if (dval > 0.0) {
+                    val = ~val;
+                    memcpy(&dval, &val, 8);
+                } else {
+                    dval *= -1.0;
+                }
             }
 
             value.v.double_value = dval;

src/sas/readstat_sas7bcat_write.c

@@ -76,8 +76,14 @@ static sas7bcat_block_t *sas7bcat_block_for_label_set(readstat_label_set_t *r_la
             memcpy(&lbp1[14], value_label->string_key, string_len);
         } else {
             uint64_t big_endian_value;
-            double double_value = -1.0 * value_label->double_key;
-            memcpy(&big_endian_value, &double_value, sizeof(double));
+            double double_value = value_label->double_key;
+            if (double_value >= 0.0) {
+                double_value *= -1.0;
+                memcpy(&big_endian_value, &double_value, sizeof(double));
+            } else {
+                memcpy(&big_endian_value, &double_value, sizeof(double));
+                big_endian_value = ~big_endian_value;
+            }
             if (machine_is_little_endian()) {
                 big_endian_value = byteswap8(big_endian_value);
             }