+/*
+ * set (initialize) the size entries in the per-file sum_struct
+ * calulating dynamic block ans checksum sizes.
+ *
+ * This is only called from generate_and_send_sums() but is a seperate
+ * function to encapsulate the logic.
+ *
+ * The block size is a rounded square root of file length.
+ *
+ * The checksum size is determined according to:
+ * blocksum_bits = BLOCKSUM_EXP + 2*log2(file_len) - log2(block_len)
+ * provided by Donovan Baarda which gives a probability of rsync
+ * algorithm corrupting data and falling back using the whole md4
+ * checksums.
+ *
+ * This might be made one of several selectable heuristics.
+ */
+
+static void sum_sizes_sqroot(struct sum_struct *sum, uint64 len)
+{
+ extern unsigned int block_size;
+ unsigned int blength;
+ int s2length;
+ uint32 c;
+ uint64 l;
+
+ if (block_size) {
+ blength = block_size;
+ } else if (len <= BLOCK_SIZE * BLOCK_SIZE) {
+ blength = BLOCK_SIZE;
+ } else {
+ l = len;
+ c = 1;
+ while (l >>= 2) {
+ c <<= 1;
+ }
+ blength = 0;
+ do {
+ blength |= c;
+ if (len < (uint64)blength * blength)
+ blength &= ~c;
+ c >>= 1;
+ } while (c >= 8); /* round to multiple of 8 */
+ blength = MAX(blength, BLOCK_SIZE);
+ }
+
+ if (protocol_version < 27) {
+ s2length = csum_length;
+ } else if (csum_length == SUM_LENGTH) {
+ s2length = SUM_LENGTH;
+ } else {
+ int b = BLOCKSUM_BIAS;
+ l = len;
+ while (l >>= 1) {
+ b += 2;
+ }
+ c = blength;
+ while (c >>= 1 && b) {
+ b--;
+ }
+ s2length = (b + 1 - 32 + 7) / 8; /* add a bit,
+ * subtract rollsum,
+ * round up
+ * --optimize in compiler--
+ */
+ s2length = MAX(s2length, csum_length);
+ s2length = MIN(s2length, SUM_LENGTH);
+ }
+
+ sum->flength = len;
+ sum->blength = blength;
+ sum->s2length = s2length;
+ sum->count = (len + (blength - 1)) / blength;
+ sum->remainder = (len % blength);