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Fix sign-extension in FNV-1/FNV-1a byte processing; add std::byte support #4

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Merged
rwindegger merged 3 commits into from
Mar 22, 2026
Merged

Fix sign-extension in FNV-1/FNV-1a byte processing; add std::byte support #4

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d0c52bc
Initial plan
Copilot Mar 22, 2026
fcbd2d5
Handle std::byte via std::to_integer and add high-byte value tests
Copilot Mar 22, 2026
14c987a
Use signed char in high_byte_values_test to directly exercise sign-ex…
Copilot Mar 22, 2026
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11 changes: 10 additions & 1 deletion include/hash23/fnv_1.h
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Original file line number Diff line number Diff line change
Expand Up @@ -5,8 +5,10 @@
#pragma once

#include <cstddef>
#include <cstdint>
#include <ranges>
#include <span>
#include <type_traits>

namespace hash23 {
class fnv_1 {
Expand Down Expand Up @@ -37,8 +39,15 @@ namespace hash23 {
requires std::ranges::contiguous_range<T>
constexpr void update(T const &data) {
for (auto const &byte : data) {
using value_type = std::remove_cvref_t<decltype(byte)>;
std::uint8_t b;
if constexpr (std::is_same_v<value_type, std::byte>) {
b = std::to_integer<std::uint8_t>(byte);
} else {
b = static_cast<std::uint8_t>(byte);
}
hash_ *= prime();
hash_ ^= static_cast<std::uint8_t>(byte);
hash_ ^= b;
}
}

Expand Down
11 changes: 10 additions & 1 deletion include/hash23/fnv_1a.h
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Original file line number Diff line number Diff line change
Expand Up @@ -5,8 +5,10 @@
#pragma once

#include <cstddef>
#include <cstdint>
#include <ranges>
#include <span>
#include <type_traits>

namespace hash23 {
class fnv_1a {
Expand Down Expand Up @@ -37,7 +39,14 @@ namespace hash23 {
requires std::ranges::contiguous_range<T>
constexpr void update(T const &data) {
for (auto const &byte: data) {
hash_ ^= static_cast<std::uint8_t>(byte);
using value_type = std::remove_cvref_t<decltype(byte)>;
std::uint8_t b;
if constexpr (std::is_same_v<value_type, std::byte>) {
b = std::to_integer<std::uint8_t>(byte);
} else {
b = static_cast<std::uint8_t>(byte);
}
hash_ ^= b;
hash_ *= prime();
}
}
Expand Down
31 changes: 31 additions & 0 deletions tests/fnv_1_tests.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -4,7 +4,9 @@

#include <gtest/gtest.h>
#include <hash23/hash23.h>
#include <cstddef>
#include <string>
#include <vector>

namespace {
TEST(fnv_1, single_block_test) {
Expand Down Expand Up @@ -39,4 +41,33 @@ namespace {
EXPECT_EQ(expected, actual);
}
}

TEST(fnv_1, high_byte_values_test) {
std::vector<signed char> const data = {
static_cast<signed char>(0x80), static_cast<signed char>(0xAB),
static_cast<signed char>(0xFF), 0x00, 0x7F
};
auto const actual = hash23::fnv_1::calculate(data);
if constexpr (sizeof(std::size_t) == 4) {
constexpr std::size_t expected = 0x4430384auz;
EXPECT_EQ(expected, actual);
} else {
constexpr std::size_t expected = 0xeaadd0afbf431feauz;
EXPECT_EQ(expected, actual);
}
}

TEST(fnv_1, std_byte_test) {
std::vector<std::byte> const data = {
std::byte{0x80}, std::byte{0xAB}, std::byte{0xFF}, std::byte{0x00}, std::byte{0x7F}
};
auto const actual = hash23::fnv_1::calculate(data);
if constexpr (sizeof(std::size_t) == 4) {
constexpr std::size_t expected = 0x4430384auz;
EXPECT_EQ(expected, actual);
} else {
constexpr std::size_t expected = 0xeaadd0afbf431feauz;
EXPECT_EQ(expected, actual);
}
}
}
31 changes: 31 additions & 0 deletions tests/fnv_1a_tests.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -4,7 +4,9 @@

#include <gtest/gtest.h>
#include <hash23/hash23.h>
#include <cstddef>
#include <string>
#include <vector>

namespace {
TEST(fnv_1a, single_block_test) {
Expand Down Expand Up @@ -39,4 +41,33 @@ namespace {
EXPECT_EQ(expected, actual);
}
}

TEST(fnv_1a, high_byte_values_test) {
std::vector<signed char> const data = {
static_cast<signed char>(0x80), static_cast<signed char>(0xAB),
static_cast<signed char>(0xFF), 0x00, 0x7F
};
auto const actual = hash23::fnv_1a::calculate(data);
if constexpr (sizeof(std::size_t) == 4) {
constexpr std::size_t expected = 0x9036aaacuz;
EXPECT_EQ(expected, actual);
} else {
constexpr std::size_t expected = 0x6b576bf0e27fc9acuz;
EXPECT_EQ(expected, actual);
}
}

TEST(fnv_1a, std_byte_test) {
std::vector<std::byte> const data = {
std::byte{0x80}, std::byte{0xAB}, std::byte{0xFF}, std::byte{0x00}, std::byte{0x7F}
};
auto const actual = hash23::fnv_1a::calculate(data);
if constexpr (sizeof(std::size_t) == 4) {
constexpr std::size_t expected = 0x9036aaacuz;
EXPECT_EQ(expected, actual);
} else {
constexpr std::size_t expected = 0x6b576bf0e27fc9acuz;
EXPECT_EQ(expected, actual);
}
}
}