Don't assume that "char" is signed.

For the C standard char can be either signed or unsigned, it's up to the
compiler, but Redis assumed that it was signed in a few places.

The practical effect of this patch is that now Redis 2.6 will run
correctly in every system where char is unsigned, notably the RaspBerry
PI and other ARM systems with GCC.

Thanks to Georgi Marinov (@eesn on twitter) that reported the problem
and allowed me to use his RaspBerry via SSH to trace and fix the issue!

src/bitops.c

@@ -114,14 +114,14 @@ void setbitCommand(redisClient *c) {
     o->ptr = sdsgrowzero(o->ptr,byte+1);
 
     /* Get current values */
-    byteval = ((char*)o->ptr)[byte];
+    byteval = ((uint8_t*)o->ptr)[byte];
     bit = 7 - (bitoffset & 0x7);
     bitval = byteval & (1 << bit);
 
     /* Update byte with new bit value and return original value */
     byteval &= ~(1 << bit);
     byteval |= ((on & 0x1) << bit);
-    ((char*)o->ptr)[byte] = byteval;
+    ((uint8_t*)o->ptr)[byte] = byteval;
     signalModifiedKey(c->db,c->argv[1]);
     server.dirty++;
     addReply(c, bitval ? shared.cone : shared.czero);
@@ -148,7 +148,7 @@ void getbitCommand(redisClient *c) {
             bitval = llbuf[byte] & (1 << bit);
     } else {
         if (byte < sdslen(o->ptr))
-            bitval = ((char*)o->ptr)[byte] & (1 << bit);
+            bitval = ((uint8_t*)o->ptr)[byte] & (1 << bit);
     }
 
     addReply(c, bitval ? shared.cone : shared.czero);

src/ziplist.c

@@ -317,15 +317,15 @@ static void zipSaveInteger(unsigned char *p, int64_t value, unsigned char encodi
     int32_t i32;
     int64_t i64;
     if (encoding == ZIP_INT_8B) {
-        ((char*)p)[0] = (char)value;
+        ((int8_t*)p)[0] = (int8_t)value;
     } else if (encoding == ZIP_INT_16B) {
         i16 = value;
         memcpy(p,&i16,sizeof(i16));
         memrev16ifbe(p);
     } else if (encoding == ZIP_INT_24B) {
         i32 = value<<8;
         memrev32ifbe(&i32);
-        memcpy(p,((unsigned char*)&i32)+1,sizeof(i32)-sizeof(int8_t));
+        memcpy(p,((uint8_t*)&i32)+1,sizeof(i32)-sizeof(uint8_t));
     } else if (encoding == ZIP_INT_32B) {
         i32 = value;
         memcpy(p,&i32,sizeof(i32));
@@ -347,7 +347,7 @@ static int64_t zipLoadInteger(unsigned char *p, unsigned char encoding) {
     int32_t i32;
     int64_t i64, ret = 0;
     if (encoding == ZIP_INT_8B) {
-        ret = ((char*)p)[0];
+        ret = ((int8_t*)p)[0];
     } else if (encoding == ZIP_INT_16B) {
         memcpy(&i16,p,sizeof(i16));
         memrev16ifbe(&i16);
@@ -358,7 +358,7 @@ static int64_t zipLoadInteger(unsigned char *p, unsigned char encoding) {
         ret = i32;
     } else if (encoding == ZIP_INT_24B) {
         i32 = 0;
-        memcpy(((unsigned char*)&i32)+1,p,sizeof(i32)-sizeof(int8_t));
+        memcpy(((uint8_t*)&i32)+1,p,sizeof(i32)-sizeof(uint8_t));
         memrev32ifbe(&i32);
         ret = i32>>8;
     } else if (encoding == ZIP_INT_64B) {