From 1d57a5fe543aee78acd1e21a7639e94010079306 Mon Sep 17 00:00:00 2001
From: Jack Lloyd <jack@randombit.net>
Date: Tue, 19 Sep 2017 12:38:53 -0400
Subject: Add basic tests for const time utils

Remove CT::min and CT::max which were unused and it turns out, broken.
---
 src/lib/utils/ct_utils.h | 38 ++++++++++----------------------------
 1 file changed, 10 insertions(+), 28 deletions(-)

(limited to 'src/lib')

diff --git a/src/lib/utils/ct_utils.h b/src/lib/utils/ct_utils.h
index 709b6d9e5..1a88cee20 100644
--- a/src/lib/utils/ct_utils.h
+++ b/src/lib/utils/ct_utils.h
@@ -94,6 +94,12 @@ inline T expand_mask(T x)
    return r;
    }
 
+template<typename T>
+inline T expand_top_bit(T a)
+   {
+   return expand_mask<T>(a >> (sizeof(T)*8-1));
+   }
+
 template<typename T>
 inline T select(T mask, T from0, T from1)
    {
@@ -119,19 +125,15 @@ inline T is_equal(T x, T y)
    }
 
 template<typename T>
-inline T is_less(T x, T y)
+inline T is_less(T a, T b)
    {
-   /*
-   This expands to a constant time sequence with GCC 5.2.0 on x86-64
-   but something more complicated may be needed for portable const time.
-   */
-   return expand_mask<T>(x < y);
+   return expand_top_bit(a ^ ((a^b) | ((a-b)^a)));
    }
 
 template<typename T>
-inline T is_lte(T x, T y)
+inline T is_lte(T a, T b)
    {
-   return expand_mask<T>(x <= y);
+   return CT::is_less(a, b) | CT::is_equal(a, b);
    }
 
 template<typename T>
@@ -163,26 +165,6 @@ inline void cond_zero_mem(T cond,
       }
    }
 
-template<typename T>
-inline T expand_top_bit(T a)
-   {
-   return expand_mask<T>(a >> (sizeof(T)*8-1));
-   }
-
-template<typename T>
-inline T max(T a, T b)
-   {
-   const T a_larger = b - a; // negative if a is larger
-   return select(expand_top_bit(a), a, b);
-   }
-
-template<typename T>
-inline T min(T a, T b)
-   {
-   const T a_larger = b - a; // negative if a is larger
-   return select(expand_top_bit(b), b, a);
-   }
-
 inline secure_vector<uint8_t> strip_leading_zeros(const uint8_t in[], size_t length)
    {
    size_t leading_zeros = 0;
-- 
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