initial pintos checkin

1 files changed, 189 insertions, 0 deletions

diff --git a/pintos-progos/lib/arithmetic.c b/pintos-progos/lib/arithmetic.c
new file mode 100644
index 0000000..bfc9b5a
--- /dev/null
+++ b/pintos-progos/lib/arithmetic.c
@@ -0,0 +1,189 @@
+#include <stdint.h>
+
+/* On x86, division of one 64-bit integer by another cannot be
+   done with a single instruction or a short sequence.  Thus, GCC
+   implements 64-bit division and remainder operations through
+   function calls.  These functions are normally obtained from
+   libgcc, which is automatically included by GCC in any link
+   that it does.
+
+   Some x86-64 machines, however, have a compiler and utilities
+   that can generate 32-bit x86 code without having any of the
+   necessary libraries, including libgcc.  Thus, we can make
+   Pintos work on these machines by simply implementing our own
+   64-bit division routines, which are the only routines from
+   libgcc that Pintos requires.
+
+   Completeness is another reason to include these routines.  If
+   Pintos is completely self-contained, then that makes it that
+   much less mysterious. */
+
+/* Uses x86 DIVL instruction to divide 64-bit N by 32-bit D to
+   yield a 32-bit quotient.  Returns the quotient.
+   Traps with a divide error (#DE) if the quotient does not fit
+   in 32 bits. */
+static inline uint32_t
+divl (uint64_t n, uint32_t d)
+{
+  uint32_t n1 = n >> 32;
+  uint32_t n0 = n;
+  uint32_t q, r;
+
+  asm ("divl %4"
+       : "=d" (r), "=a" (q)
+       : "0" (n1), "1" (n0), "rm" (d));
+
+  return q;
+}
+
+/* Returns the number of leading zero bits in X,
+   which must be nonzero. */
+static int
+nlz (uint32_t x) 
+{
+  /* This technique is portable, but there are better ways to do
+     it on particular systems.  With sufficiently new enough GCC,
+     you can use __builtin_clz() to take advantage of GCC's
+     knowledge of how to do it.  Or you can use the x86 BSR
+     instruction directly. */
+  int n = 0;
+  if (x <= 0x0000FFFF)
+    {
+      n += 16;
+      x <<= 16; 
+    }
+  if (x <= 0x00FFFFFF)
+    {
+      n += 8;
+      x <<= 8; 
+    }
+  if (x <= 0x0FFFFFFF)
+    {
+      n += 4;
+      x <<= 4;
+    }
+  if (x <= 0x3FFFFFFF)
+    {
+      n += 2;
+      x <<= 2; 
+    }
+  if (x <= 0x7FFFFFFF)
+    n++;
+  return n;
+}
+
+/* Divides unsigned 64-bit N by unsigned 64-bit D and returns the
+   quotient. */
+static uint64_t
+udiv64 (uint64_t n, uint64_t d)
+{
+  if ((d >> 32) == 0) 
+    {
+      /* Proof of correctness:
+
+         Let n, d, b, n1, and n0 be defined as in this function.
+         Let [x] be the "floor" of x.  Let T = b[n1/d].  Assume d
+         nonzero.  Then:
+             [n/d] = [n/d] - T + T
+                   = [n/d - T] + T                         by (1) below
+                   = [(b*n1 + n0)/d - T] + T               by definition of n
+                   = [(b*n1 + n0)/d - dT/d] + T
+                   = [(b(n1 - d[n1/d]) + n0)/d] + T
+                   = [(b[n1 % d] + n0)/d] + T,             by definition of %
+         which is the expression calculated below.
+
+         (1) Note that for any real x, integer i: [x] + i = [x + i].
+
+         To prevent divl() from trapping, [(b[n1 % d] + n0)/d] must
+         be less than b.  Assume that [n1 % d] and n0 take their
+         respective maximum values of d - 1 and b - 1:
+                 [(b(d - 1) + (b - 1))/d] < b
+             <=> [(bd - 1)/d] < b
+             <=> [b - 1/d] < b
+         which is a tautology.
+
+         Therefore, this code is correct and will not trap. */
+      uint64_t b = 1ULL << 32;
+      uint32_t n1 = n >> 32;
+      uint32_t n0 = n; 
+      uint32_t d0 = d;
+
+      return divl (b * (n1 % d0) + n0, d0) + b * (n1 / d0); 
+    }
+  else 
+    {
+      /* Based on the algorithm and proof available from
+         http://www.hackersdelight.org/revisions.pdf. */
+      if (n < d)
+        return 0;
+      else 
+        {
+          uint32_t d1 = d >> 32;
+          int s = nlz (d1);
+          uint64_t q = divl (n >> 1, (d << s) >> 32) >> (31 - s);
+          return n - (q - 1) * d < d ? q - 1 : q; 
+        }
+    }
+}
+
+/* Divides unsigned 64-bit N by unsigned 64-bit D and returns the
+   remainder. */
+static uint32_t
+umod64 (uint64_t n, uint64_t d)
+{
+  return n - d * udiv64 (n, d);
+}
+
+/* Divides signed 64-bit N by signed 64-bit D and returns the
+   quotient. */
+static int64_t
+sdiv64 (int64_t n, int64_t d)
+{
+  uint64_t n_abs = n >= 0 ? (uint64_t) n : -(uint64_t) n;
+  uint64_t d_abs = d >= 0 ? (uint64_t) d : -(uint64_t) d;
+  uint64_t q_abs = udiv64 (n_abs, d_abs);
+  return (n < 0) == (d < 0) ? (int64_t) q_abs : -(int64_t) q_abs;
+}
+
+/* Divides signed 64-bit N by signed 64-bit D and returns the
+   remainder. */
+static int32_t
+smod64 (int64_t n, int64_t d)
+{
+  return n - d * sdiv64 (n, d);
+}
+
+/* These are the routines that GCC calls. */
+
+long long __divdi3 (long long n, long long d);
+long long __moddi3 (long long n, long long d);
+unsigned long long __udivdi3 (unsigned long long n, unsigned long long d);
+unsigned long long __umoddi3 (unsigned long long n, unsigned long long d);
+
+/* Signed 64-bit division. */
+long long
+__divdi3 (long long n, long long d) 
+{
+  return sdiv64 (n, d);
+}
+
+/* Signed 64-bit remainder. */
+long long
+__moddi3 (long long n, long long d) 
+{
+  return smod64 (n, d);
+}
+
+/* Unsigned 64-bit division. */
+unsigned long long
+__udivdi3 (unsigned long long n, unsigned long long d) 
+{
+  return udiv64 (n, d);
+}
+
+/* Unsigned 64-bit remainder. */
+unsigned long long
+__umoddi3 (unsigned long long n, unsigned long long d) 
+{
+  return umod64 (n, d);
+}