1 files changed, 92 insertions, 0 deletions

diff --git a/private/ntos/rtl/recip.c b/private/ntos/rtl/recip.c
new file mode 100644
index 000000000..603aeea24
--- /dev/null
+++ b/private/ntos/rtl/recip.c
@@ -0,0 +1,92 @@
+/*++
+
+Copyright (c) 1989  Microsoft Corporation
+
+Module Name:
+
+    recip.c
+
+Abstract:
+
+    This module generates reciprocol fractions for implementing integer
+    division by multiplication.
+
+Author:
+
+    David N. Cutler (davec) 13-May-1989
+
+Environment:
+
+    User mode.
+
+Revision History:
+
+--*/
+
+#include <stdio.h>
+
+typedef struct _large_integer {
+    unsigned long LowPart;
+    long HighPart;
+    } large_integer;
+
+//long Divisors[] = {2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096, 8192, 0};
+long Divisors[] = {10, 10000, 10000000, 86400000, 0};
+
+void
+main (argc, argv)
+    int argc;
+    char *argv[];
+{
+
+    large_integer Fraction;
+    long Index;
+    long NumberBits;
+    long Remainder;
+
+    long i;
+
+    //
+    // Compute first few reciprocols.
+    //
+
+    for (Index = Divisors[i = 0]; Index != 0L; Index = Divisors[++i]) {
+        NumberBits = 0L;
+        Remainder = 1L;
+        Fraction.LowPart = 0L;
+        Fraction.HighPart = 0L;
+        while (Fraction.HighPart >= 0L) {
+            NumberBits += 1L;
+            Fraction.HighPart <<= 1L;
+            if ((Fraction.LowPart & 0x80000000) != 0L) {
+                Fraction.HighPart += 1L;
+            }
+            Fraction.LowPart <<= 1L;
+            Remainder <<= 1L;
+            if (Remainder >= Index) {
+                Remainder -= Index;
+                Fraction.LowPart |= 1L;
+            }
+        }
+        if (Remainder) {
+            if ((Fraction.LowPart == -1L) && (Fraction.HighPart == -1L)) {
+                Fraction.LowPart = 0L;
+                Fraction.HighPart = 0x80000000;
+                NumberBits -= 1L;
+            } else {
+                if (Fraction.LowPart == -1L) {
+                    Fraction.LowPart = 0L;
+                    Fraction.HighPart += 1L;
+                } else {
+                    Fraction.LowPart += 1L;
+                }
+            }
+        }
+
+        printf("Divisor %2ld,  Fraction %8lx, %8lx Shift  %ld\n", Index,
+               Fraction.HighPart, Fraction.LowPart, NumberBits - 64L);
+    }
+
+    return;
+}
+