Review: Remove long_u: memfile: Refactor: blocknr_T: long -> int64_t.

Replace long with int64_t.
Apart from being convenient, not using long is required by clint.

src/nvim/memfile.c

@@ -129,12 +129,16 @@ memfile_T *mf_open(char_u *fname, int flags)
   // must be rounded up.
   if (mfp->mf_fd < 0
       || (flags & (O_TRUNC|O_EXCL))
-      || (size = lseek(mfp->mf_fd, (off_t)0L, SEEK_END)) <= 0)
+      || (size = lseek(mfp->mf_fd, (off_t)0L, SEEK_END)) <= 0) {
     // no file or empty file
     mfp->mf_blocknr_max = 0;
-  else
+  } else {
-    mfp->mf_blocknr_max = (blocknr_T)((size + mfp->mf_page_size - 1)
+    assert(sizeof(off_t) <= sizeof(blocknr_T)
-                                      / mfp->mf_page_size);
+           && mfp->mf_page_size > 0
+           && mfp->mf_page_size - 1 <= INT64_MAX - size);
+    mfp->mf_blocknr_max = (((blocknr_T)size + mfp->mf_page_size - 1)
+                           / mfp->mf_page_size);
+  }
   mfp->mf_blocknr_min = -1;
   mfp->mf_neg_count = 0;
   mfp->mf_infile_count = mfp->mf_blocknr_max;
@@ -151,8 +155,8 @@ memfile_T *mf_open(char_u *fname, int flags)
       --shift;
     }
 
-    assert(p_mm << shift >= p_mm);  // check we don't overflow
+    assert(p_mm <= LONG_MAX >> shift);  // check we don't overflow
-    assert(p_mm < UINT_MAX);        // check we can cast to unsigned
+    assert((uintmax_t)(p_mm << shift) <= UINT_MAX);  // check we can cast safely
     mfp->mf_used_count_max = (unsigned)(p_mm << shift) / page_size;
     if (mfp->mf_used_count_max < 10)
       mfp->mf_used_count_max = 10;
@@ -706,12 +710,15 @@ static int mf_read(memfile_T *mfp, bhdr_T *hp)
     return FAIL;
 
   unsigned page_size = mfp->mf_page_size;
-  off_t offset = (off_t)page_size * hp->bh_bnum;
+  // TODO(elmart): Check (page_size * hp->bh_bnum) within off_t bounds.
-  unsigned size = page_size * hp->bh_page_count;
+  off_t offset = (off_t)(page_size * hp->bh_bnum);
   if (lseek(mfp->mf_fd, offset, SEEK_SET) != offset) {
     PERROR(_("E294: Seek error in swap file read"));
     return FAIL;
   }
+  // check for overflow; we know that page_size must be > 0
+  assert(hp->bh_page_count <= UINT_MAX / page_size);
+  unsigned size = page_size * hp->bh_page_count;
   if ((unsigned)read_eintr(mfp->mf_fd, hp->bh_data, size) != size) {
     PERROR(_("E295: Read error in swap file"));
     return FAIL;
@@ -758,7 +765,8 @@ static int mf_write(memfile_T *mfp, bhdr_T *hp)
     } else
       hp2 = hp;
 
-    offset = (off_t)page_size * nr;
+    // TODO(elmart): Check (page_size * nr) within off_t bounds.
+    offset = (off_t)(page_size * nr);
     if (lseek(mfp->mf_fd, offset, SEEK_SET) != offset) {
       PERROR(_("E296: Seek error in swap file write"));
       return FAIL;

src/nvim/memfile_defs.h

@@ -11,7 +11,7 @@
 /// Blocks numbered from 0 upwards have been assigned a place in the actual
 /// file. The block number is equal to the page number in the file. The blocks
 /// with negative numbers are currently in memory only.
-typedef long blocknr_T;
+typedef int64_t blocknr_T;
 
 /// A hash item.
 ///

src/nvim/memline.c

@@ -639,7 +639,7 @@ static void ml_upd_block0(buf_T *buf, upd_block0_T what)
   ZERO_BL     *b0p;
 
   mfp = buf->b_ml.ml_mfp;
-  if (mfp == NULL || (hp = mf_get(mfp, (blocknr_T)0, 1)) == NULL)
+  if (mfp == NULL || (hp = mf_get(mfp, 0, 1)) == NULL)
     return;
   b0p = hp->bh_data;
   if (ml_check_b0_id(b0p) == FAIL)
@@ -867,7 +867,7 @@ void ml_recover(void)
   /*
    * try to read block 0
    */
-  if ((hp = mf_get(mfp, (blocknr_T)0, 1)) == NULL) {
+  if ((hp = mf_get(mfp, 0, 1)) == NULL) {
     msg_start();
     MSG_PUTS_ATTR(_("Unable to read block 0 from "), attr | MSG_HIST);
     msg_outtrans_attr(mfp->mf_fname, attr | MSG_HIST);
@@ -925,7 +925,7 @@ void ml_recover(void)
     if ((size = lseek(mfp->mf_fd, (off_t)0L, SEEK_END)) <= 0)
       mfp->mf_blocknr_max = 0;              /* no file or empty file */
     else
-      mfp->mf_blocknr_max = (blocknr_T)(size / mfp->mf_page_size);
+      mfp->mf_blocknr_max = size / mfp->mf_page_size;
     mfp->mf_infile_count = mfp->mf_blocknr_max;
 
     /* need to reallocate the memory used to store the data */
@@ -1031,7 +1031,7 @@ void ml_recover(void)
     /*
      * get block
      */
-    if ((hp = mf_get(mfp, (blocknr_T)bnum, page_count)) == NULL) {
+    if ((hp = mf_get(mfp, bnum, page_count)) == NULL) {
       if (bnum == 1) {
         EMSG2(_("E309: Unable to read block 1 from %s"), mfp->mf_fname);
         goto theend;