diff --git a/doc/TXTH.md b/doc/TXTH.md
index 49cca054..6c694878 100644
--- a/doc/TXTH.md
+++ b/doc/TXTH.md
@@ -53,7 +53,7 @@ The following can be used in place of `(value)` for `(key) = (value)` commands.
 - `(other)`: other special values for certain keys, described per key
 
 
-The above may be combined with math operations (+-*/): `(key) = (number) (op) (offset) (op) (field) (...)`
+The above may be combined with math operations (+-*/&): `(key) = (number) (op) (offset) (op) (field) (...)`
 
 ### KEYS
 
@@ -240,7 +240,7 @@ Modifies the meaning of sample fields when set *before* them.
 
 Accepted values:
 - `samples`: exact sample (default)
-- `bytes`: automatically converts bytes/offset to samples (applies after */+- modifiers)
+- `bytes`: automatically converts bytes/offset to samples (applies after */+-& modifiers)
 - `blocks`: same as bytes, but value is given in blocks/frames
   * Value is internally converted from blocks to bytes first: `bytes = (value * interleave*channels)`
 
@@ -520,13 +520,13 @@ sample_rate = 0x04      # sample rate is the same for all subsongs
 ```
 
 ### Math
-Sometimes header values are in "sectors" or similar concepts (typical in DVD games), and need to be adjusted to a real value.
+Sometimes header values are in "sectors" or similar concepts (typical in DVD games), and need to be adjusted to a real value using some complex math:
 ```
 sample_type   = bytes
 start_offset  = @0x10 * 0x800    # 0x15 * DVD sector size, for example
 ```
 
-You can also use certain fields' values:
+You can use `+-*/&` operators, and also certain fields' values:
 ```
 num_samples = @0x10 * channels  # byte-to-samples of channel_size
 ```
@@ -825,3 +825,17 @@ PAD.XAG   : 0x150
 JIN002.XAG: 0x168
 JIN003.XAG: 0x180
 ```
+
+
+** Grandia (PS1) **
+```
+header_file       = GM1.IDX
+body_file         = GM1.STZ
+
+subsong_count     = 394  #last doesn't have size though
+subsong_offset    = 0x04
+
+subfile_offset    = (@0x00 & 0xFFFFF) * 0x800
+subfile_extension = seb
+subfile_size      = ((@0x04 - @0x00) & 0xFFFFF) * 0x800
+```
diff --git a/src/meta/txth.c b/src/meta/txth.c
index 8c85bda7..6b0d0ae6 100644
--- a/src/meta/txth.c
+++ b/src/meta/txth.c
@@ -593,7 +593,8 @@ static VGMSTREAM *init_subfile(txth_header * txth) {
         vgmstream_force_loop(vgmstream, 0, 0, 0);
     }
 
-    if (txth->chunk_count && txth->subsong_count) {
+    /* assumes won't point to subfiles with subsongs */
+    if (/*txth->chunk_count &&*/ txth->subsong_count) {
         vgmstream->num_streams = txth->subsong_count;
     }
     //todo: other combos with subsongs + subfile?
@@ -1256,7 +1257,7 @@ static int is_substring(const char * val, const char * cmp, int inline_field) {
     chr = val[len];
 
     /* "val" can end with math for inline fields (like interleave*0x10) */
-    if (inline_field && (chr == '+' || chr == '-' || chr == '*' || chr == '/'))
+    if (inline_field && (chr == '+' || chr == '-' || chr == '*' || chr == '/' || chr == '&'))
         return len;
 
     /* otherwise "val" ends in space or eof (to tell "interleave" and "interleave_last" apart) */
@@ -1532,7 +1533,7 @@ static int parse_num(STREAMFILE * streamFile, txth_header * txth, const char * v
             brackets--;
             n = 1;
         }
-        else if (type == '+' || type == '-' || type == '/' || type == '*') { /* op */
+        else if (type == '+' || type == '-' || type == '/' || type == '*' || type == '&') { /* op */
             op = type;
             n = 1;
         }
@@ -1600,6 +1601,8 @@ static int parse_num(STREAMFILE * streamFile, txth_header * txth, const char * v
             else if ((n = is_string_field(val,"loop_end_sample")))      value = txth->loop_end_sample;
             else if ((n = is_string_field(val,"subsong_count")))        value = txth->subsong_count;
             else if ((n = is_string_field(val,"subsong_offset")))       value = txth->subsong_offset;
+            else if ((n = is_string_field(val,"subfile_offset")))       value = txth->subfile_offset;
+            else if ((n = is_string_field(val,"subfile_size")))       value = txth->subfile_size;
             //todo whatever, improve
             else if ((n = is_string_field(val,"name_value")))           value = txth->name_values[0];
             else if ((n = is_string_field(val,"name_value1")))          value = txth->name_values[0];
@@ -1631,6 +1634,7 @@ static int parse_num(STREAMFILE * streamFile, txth_header * txth, const char * v
                 case '-': value = result - value; break;
                 case '*': value = result * value; break;
                 case '/': if (value == 0) goto fail; value = result / value; break;
+                case '&': value = result & value; break;
                 default: break;
             }
             op = ' '; /* consume */