Merge pull request #2013 from ghaerr/watc

[libc] Add fast divmod.asm to Watcom printf

libc/stdio/vfprintf.c

@@ -227,12 +227,12 @@ vfprintf(FILE *op, const char *fmt, va_list ap)
             p = buf + sizeof(buf) - 1;
             *p = '\0';
             do {
-#ifdef __WATCOMC__
-                c = v % radix;
-                v = v / radix;
-#else
+#if 1
                 c = radix;
                 v = __divmod(v, &c);    /* remainder returned in c */
+#else
+                c = v % radix;
+                v = v / radix;
 #endif
                 if (c > 9)
                     *--p = ((*fmt == 'X')? 'A': 'a') - 10 + c;

libc/watcom/asm/divmod.asm

@@ -0,0 +1,46 @@
+; Fast 32-bit combined divide and modulo routine
+;
+; unsigned long __divmod(unsigned long val, unsigned int *baserem)
+;  Unsigned divide 32-bits by 16-bits
+;      Store denominator in *baserem before calling
+;      Returns 32-bit quotient in DX:AX and remainder in *baserem
+;
+;  Designed for a fast replacement of the following code
+;      unsigned int rem, base;
+;      rem = val % base;
+;      val = val / base;
+;  New code:
+;      rem = base;
+;      val = __divmod(val, &rem);
+;
+;  from by OpenWatcom ltoa.c __uldiv routine
+;  14 Sep 2024 Greg Haerr
+
+include mdef.inc
+include struct.inc
+
+        modstart    divmod
+
+        xdefp   "C",__divmod
+        defpe    __divmod
+
+;  divides DX:AX / [BX]
+;  returns DX:AX with remainder in [BX]
+
+        xor    cx,cx                ; temp CX = 0
+        cmp    dx,[bx]              ; is upper 16 bits numerator less than denominator
+        jb     short fast           ; yes - only one DIV needed
+        xchg   ax,dx                ; AX = upper numerator, DX = lower numerator
+        xchg   cx,dx                ; DX = 0, CX = lower numerator
+        div    word ptr [bx]        ; AX = upper numerator / base, DX = remainder
+        xchg   ax,cx                ; AX = lower numerator, CX = high quotient
+    fast:
+        div    word ptr [bx]        ; AX = lower numerator / base, DX = remainder
+        mov    [bx],dx              ; store remainder
+        mov    dx,cx                ; DX = high quotient, AX = low quotient
+        ret
+
+__divmod endp
+
+        endmod
+        end