From 875c0c2d16fbcaa61bfc46da58533ab0890bf513 Mon Sep 17 00:00:00 2001
From: Kaz Kylheku <kaz@kylheku.com>
Date: Fri, 26 Feb 2016 22:34:14 -0800
Subject: Functions for converting between buffers and integers.

These functions convert between positive integers, and
fixed-size memory buffers representing pure binary numbers in
big endian byte order.

This functionality will be used in some upcoming networking
code.

* arith.c (num_from_buffer, num_to_buffer): New functions.

* arith.h (num_from_buffer, num_to_buffer): Declared.

* mpi/mpi.c (mp_to_unsigned_buf): New function.

* mpi/mpi.h (mp_to_unsigned_buf): Declared.
---
 arith.c   | 31 +++++++++++++++++++++++++++++++
 arith.h   |  2 ++
 mpi/mpi.c | 26 ++++++++++++++++++++++++++
 mpi/mpi.h |  1 +
 4 files changed, 60 insertions(+)

diff --git a/arith.c b/arith.c
index 497aefa7..ecb3e03e 100644
--- a/arith.c
+++ b/arith.c
@@ -90,6 +90,37 @@ val bignum_from_uintptr(uint_ptr_t u)
   return n;
 }
 
+val num_from_buffer(mem_t *buf, int bytes)
+{
+  val n = make_bignum();
+  mp_read_unsigned_bin(mp(n), buf, bytes);
+  return normalize(n);
+}
+
+int num_to_buffer(val num, mem_t *buf, int bytes)
+{
+  switch (type(num)) {
+  case CHR: case NUM:
+    {
+      cnum n = coerce(cnum, num) >> TAG_SHIFT;
+      mem_t *ptr = buf + bytes;
+
+      for (; n != 0; n >>= 8) {
+        if (ptr == buf)
+          return 0;
+        *--ptr = n & 0xff;
+      }
+      while (ptr > buf)
+        *--ptr = 0;
+    }
+    return 1;
+  case BGNUM:
+    return mp_to_unsigned_buf(mp(num), buf, bytes) == MP_OKAY ? 1 : 0;
+  default:
+    type_mismatch(lit("~s is not an integer"), num, nao);
+  }
+}
+
 #if HAVE_DOUBLE_INTPTR_T
 
 static val bignum_dbl_ipt(double_intptr_t di)
diff --git a/arith.h b/arith.h
index 083a8a19..bc3a0568 100644
--- a/arith.h
+++ b/arith.h
@@ -28,6 +28,8 @@ val make_bignum(void);
 val bignum(cnum cn);
 val bignum_from_long(long l);
 val bignum_from_uintptr(uint_ptr_t u);
+val num_from_buffer(mem_t *buf, int bytes);
+int num_to_buffer(val num, mem_t *buf, int bytes);
 int highest_bit(int_ptr_t n);
 val normalize(val bignum);
 val in_int_ptr_range(val bignum);
diff --git a/mpi/mpi.c b/mpi/mpi.c
index c52e47bd..64cfb25a 100644
--- a/mpi/mpi.c
+++ b/mpi/mpi.c
@@ -3010,6 +3010,32 @@ mp_err mp_to_unsigned_bin(mp_int *mp, unsigned char *str)
 
 /* }}} */
 
+mp_err mp_to_unsigned_buf(mp_int *mp, unsigned char *str, int size)
+{
+  mp_digit      *dp, *end;
+  unsigned char *spos;
+
+  ARGCHK(mp != NULL && str != NULL && size >= 0, MP_BADARG);
+
+  for (spos = str + size, dp = DIGITS(mp), end = dp + USED(mp); dp < end; dp++) {
+    int      ix;
+    mp_digit d = *dp;
+
+    for (ix = 0; ix < (int) sizeof(mp_digit); ++ix) {
+	if (dp + 1 == end && d == 0)
+	  break;
+	ARGCHK(spos >= str, MP_RANGE);
+      *--spos = d & 0xFF;
+      d >>= 8;
+    }
+  }
+
+  while (spos > str)
+    *--spos = 0;
+
+  return MP_OKAY;
+}
+
 /* {{{ mp_count_bits(mp) */
 
 int    mp_count_bits(mp_int *mp)
diff --git a/mpi/mpi.h b/mpi/mpi.h
index 0e000643..cd7e823d 100644
--- a/mpi/mpi.h
+++ b/mpi/mpi.h
@@ -217,6 +217,7 @@ mp_err mp_to_signed_bin(mp_int *mp, unsigned char *str);
 mp_err mp_read_unsigned_bin(mp_int *mp, unsigned char *str, int len);
 int    mp_unsigned_bin_size(mp_int *mp);
 mp_err mp_to_unsigned_bin(mp_int *mp, unsigned char *str);
+mp_err mp_to_unsigned_buf(mp_int *mp, unsigned char *str, int size);
 
 int    mp_count_bits(mp_int *mp);
 int    mp_is_pow_two(mp_int *mp);
-- 
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