Merge pull request #1789 from evoskuil/master

Fix ob1 errors in ceilinged log.

Author: evoskuil

include/bitcoin/system/impl/math/bits.ipp

@@ -39,7 +39,7 @@ template <typename Value, if_unsigned_integer<Value>>
 constexpr size_t bit_width(Value value) NOEXCEPT
 {
     // zero-based position of msb.
-    return ceilinged_log2(value);
+    return is_zero(value) ? zero : add1(floored_log2(value));
 }
 
 // Called by machine::number (for to_unnegated).

include/bitcoin/system/impl/math/bytes.ipp

@@ -38,7 +38,7 @@ constexpr size_t byte_width(Integral value) NOEXCEPT
     // (zero-based position of msb) + 7 / 8.
     // (bit_width(value) + 7) / 8
     // (ceilinged_log2(value) + 7) / 8
-    return ceilinged_log256(value);
+    return is_zero(value) ? zero : add1(floored_log256(value));
 }
 
 // Called by machine::number (for little-endian chunk sizing).

include/bitcoin/system/impl/math/logarithm.ipp

@@ -53,7 +53,7 @@ constexpr Exponent ceilinged_log_(Base base, Value value) NOEXCEPT
         const auto factor = possible_narrow_and_sign_cast<Value>(base);
 
         Exponent exponent = 0;
-        while (value > 0) { ++exponent; value /= factor; }
+        while (value > 1) { ++exponent; value /= factor; }
         return exponent;
     }
 }
@@ -125,7 +125,7 @@ constexpr Exponent ceilinged_log2(Value value) NOEXCEPT
 
     // base2 integral optimization over normal form.
     return possible_narrow_and_sign_cast<Exponent>(
-        std::bit_width(to_unsigned(value)));
+        std::bit_width(sub1(to_unsigned(value))));
 }
 
 // Called by bc::bit_width.
@@ -134,12 +134,12 @@ template <typename Exponent, typename Value,
     if_non_integral_integer<Value>>
 constexpr Exponent ceilinged_log2(Value value) NOEXCEPT
 {
-    if (is_log_overflow<2>(value))
+    if (is_log_overflow<2>(value) || is_one(value))
         return 0;
 
     // base2 uintx optimization over normal form.
     return possible_narrow_and_sign_cast<Exponent>(
-        add1(mp::msb(value)));
+        add1(mp::msb(value - 1)));
 }
 
 // Called by bc::byte_width.
@@ -159,24 +159,24 @@ constexpr Exponent ceilinged_log256(Value value) NOEXCEPT
 
     if constexpr (size == sizeof(uint64_t))
     {
-        if (compare > 0x00ffffffffffffff_u64) return 8;
-        if (compare > 0x0000ffffffffffff_u64) return 7;
-        if (compare > 0x000000ffffffffff_u64) return 6;
-        if (compare > 0x00000000ffffffff_u64) return 5;
+        if (compare > 0x0100000000000000_u64) return 8;
+        if (compare > 0x0001000000000000_u64) return 7;
+        if (compare > 0x0000010000000000_u64) return 6;
+        if (compare > 0x0000000100000000_u64) return 5;
     }
 
     if constexpr (size >= sizeof(uint32_t))
     {
-        if (compare > 0x00ffffff_u32) return 4;
-        if (compare > 0x0000ffff_u32) return 3;
+        if (compare > 0x01000000_u32) return 4;
+        if (compare > 0x00010000_u32) return 3;
     }
 
     if constexpr (size >= sizeof(uint16_t))
     {
-        if (compare > 0x00ff_u16) return 2;
+        if (compare > 0x0100_u16) return 2;
     }
 
-    return (compare > 0x00_u8) ? 1 : 0;
+    return (compare > 0x01_u8) ? 1 : 0;
 }
 
 // Called by bc::byte_width.

test/chain/block.cpp

@@ -780,7 +780,7 @@ BOOST_AUTO_TEST_CASE(block__merkle_branch__medium_power_of_two__expected)
 BOOST_AUTO_TEST_CASE(block__merkle_branch__power_of_two_minus_one__expected)
 {
     constexpr auto leaf = 1023u;
-    constexpr auto size = sub1(ceilinged_log2(add1(leaf)));
+    constexpr auto size = ceilinged_log2(add1(leaf));
     const auto branch = block::merkle_branch(leaf, add1(leaf));
     BOOST_REQUIRE_EQUAL(branch.size(), size);
     BOOST_REQUIRE_EQUAL(branch.front().sibling, 1022u);
@@ -792,7 +792,7 @@ BOOST_AUTO_TEST_CASE(block__merkle_branch__power_of_two_minus_one__expected)
 BOOST_AUTO_TEST_CASE(block__merkle_branch__odd_large_leaf_with_duplication__expected)
 {
     constexpr auto leaf = 2047u;
-    constexpr auto size = sub1(ceilinged_log2(add1(leaf)));
+    constexpr auto size = ceilinged_log2(add1(leaf));
     const auto branch = block::merkle_branch(leaf, add1(leaf));
     BOOST_REQUIRE_EQUAL(branch.size(), size);
     BOOST_REQUIRE_EQUAL(branch.front().sibling, 2046u);

test/chain/compact.cpp

@@ -261,14 +261,11 @@ static_assert(compact::expand(compact::compress(uint256_t(42))) == uint256_t(42)
 //    (exponent > 32 && mantissa > 0x00ffff)    // strict  (33 with 1|2)
 //)
 
-// > 0x0000 <= 0x00ff (overflow if exponent > 31 and ceilinged_log256(mantissa) > 1)
-static_assert(ceilinged_log256(0x00000001ul) == 1);
-static_assert(ceilinged_log256(0x000000fful) == 1);
+// > 0x0000 <= 0x00ff (overflow if exponent > 31 and byte_width(mantissa) > 1)
+static_assert(byte_width(0x000000fful) == 1);
 
-// > 0x00ff <= 0x0000ffff (eoverflow if exponent > 30 and ceilinged_log256(mantissa) > 2)
-static_assert(ceilinged_log256(0x00000100ul) == 2);
-static_assert(ceilinged_log256(0x0000fffful) == 2);
+// > 0x00ff <= 0x0000ffff (overflow if exponent > 30 and byte_width(mantissa) > 2)
+static_assert(byte_width(0x0000fffful) == 2);
 
-// > 0x0000ffff (<= 0x007ffffful) (overflow if exponent > 29 and ceilinged_log256(mantissa) > 3)
-static_assert(ceilinged_log256(0x00010000ul) == 3);
-static_assert(ceilinged_log256(0x007ffffful) == 3);
+// > 0x0000ffff (<= 0x007ffffful) (overflow if exponent > 29 and byte_width(mantissa) > 3)
+static_assert(byte_width(0x007ffffful) == 3);

test/math/bytes.cpp

@@ -20,6 +20,8 @@
 
 BOOST_AUTO_TEST_SUITE(bytes_tests)
 
+constexpr auto foo = byte_width(1_u8);
+
  // byte_width (unsigned/positive)
 static_assert(byte_width(0_u8) == 0);
 static_assert(byte_width(1_u8) == 1);