+
+ /* return recombined sums */
+ return adler | (sum2 << 16);
+}
+
+/* ========================================================================= */
+local uLong adler32_combine_(adler1, adler2, len2)
+ uLong adler1;
+ uLong adler2;
+ z_off64_t len2;
+{
+ unsigned long sum1;
+ unsigned long sum2;
+ unsigned rem;
+
+ /* for negative len, return invalid adler32 as a clue for debugging */
+ if (len2 < 0)
+ return 0xffffffffUL;
+
+ /* the derivation of this formula is left as an exercise for the reader */
+ MOD63(len2); /* assumes len2 >= 0 */
+ rem = (unsigned)len2;
+ sum1 = adler1 & 0xffff;
+ sum2 = rem * sum1;
+ MOD(sum2);
+ sum1 += (adler2 & 0xffff) + BASE - 1;
+ sum2 += ((adler1 >> 16) & 0xffff) + ((adler2 >> 16) & 0xffff) + BASE - rem;
+ if (sum1 >= BASE) sum1 -= BASE;
+ if (sum1 >= BASE) sum1 -= BASE;
+ if (sum2 >= ((unsigned long)BASE << 1)) sum2 -= ((unsigned long)BASE << 1);
+ if (sum2 >= BASE) sum2 -= BASE;
+ return sum1 | (sum2 << 16);
+}
+
+/* ========================================================================= */
+uLong ZEXPORT adler32_combine(adler1, adler2, len2)
+ uLong adler1;
+ uLong adler2;
+ z_off_t len2;
+{
+ return adler32_combine_(adler1, adler2, len2);
+}
+
+uLong ZEXPORT adler32_combine64(adler1, adler2, len2)
+ uLong adler1;
+ uLong adler2;
+ z_off64_t len2;
+{
+ return adler32_combine_(adler1, adler2, len2);