/*
 * Copyright 2022-present MongoDB, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include "mc-cmp-private.h"
#include "mc-range-encoding-private.h"
#include "mongocrypt-private.h"
#include "mongocrypt-util-private.h" // mc_isinf

#include <math.h> // pow

/* mc-range-encoding.c assumes integers are encoded with two's complement for
 * correctness. */
#if (-1 & 3) != 3
#error Error: Twos complement integer representation is required.
#endif

/**
 * Encode a signed 32-bit integer as an unsigned 32-bit integer by adding 2^31.
 * Some documentation references this as making the value "unbiased".
 */
static uint32_t encodeInt32(int32_t v) {
    // Shift the int32_t range [-2^31, 2^31 - 1] to the uint32_t range [0, 2^32].
    // new_zero is the mapped 0 value.
    uint32_t new_zero = (UINT32_C(1) << 31);

    if (v < 0) {
        // Signed integers have a value that there is no positive equivalent and
        // must be handled specially
        if (v == INT32_MIN) {
            return 0;
        }

        int32_t v_pos = v * -1;
        uint32_t v_u32 = (uint32_t)v_pos;
        return new_zero - v_u32;
    }

    uint32_t v_u32 = (uint32_t)v;
    return new_zero + v_u32;
}

bool mc_getTypeInfo32(mc_getTypeInfo32_args_t args, mc_OSTType_Int32 *out, mongocrypt_status_t *status) {
    if (args.min.set != args.max.set) {
        CLIENT_ERR("Must specify both a lower and upper bound or no bounds.");
        return false;
    }

    if (!args.min.set) {
        uint32_t v_u32 = encodeInt32(args.value);
        *out = (mc_OSTType_Int32){v_u32, 0, UINT32_MAX};
        return true;
    }

    if (args.min.value >= args.max.value) {
        CLIENT_ERR("The minimum value must be less than the maximum value, got "
                   "min: %" PRId32 ", max: %" PRId32,
                   args.min.value,
                   args.max.value);
        return false;
    }

    if (args.value > args.max.value || args.value < args.min.value) {
        CLIENT_ERR("Value must be greater than or equal to the minimum value "
                   "and less than or equal to the maximum value, got min: %" PRId32 ", max: %" PRId32
                   ", value: %" PRId32,
                   args.min.value,
                   args.max.value,
                   args.value);
        return false;
    }

    // Convert to unbiased uint32. Then subtract the min value.
    uint32_t v_u32 = encodeInt32(args.value);
    uint32_t min_u32 = encodeInt32(args.min.value);
    uint32_t max_u32 = encodeInt32(args.max.value);

    v_u32 -= min_u32;
    max_u32 -= min_u32;

    *out = (mc_OSTType_Int32){v_u32, 0, max_u32};
    return true;
}

/**
 * Encode a signed 64-bit integer as an unsigned 64-bit integer by adding 2^63.
 * Some documentation references this as making the value "unbiased".
 */
static uint64_t encodeInt64(int64_t v) {
    // Shift the int64_t range [-2^63, 2^63 - 1] to the uint64_t range [0, 2^64].
    // new_zero is the mapped 0 value.
    uint64_t new_zero = (UINT64_C(1) << 63);

    if (v < 0) {
        // Signed integers have a value that there is no positive equivalent and
        // must be handled specially
        if (v == INT64_MIN) {
            return 0;
        }

        int64_t v_pos = v * -1;
        uint64_t v_u64 = (uint64_t)v_pos;
        return new_zero - v_u64;
    }

    uint64_t v_u64 = (uint64_t)v;
    return new_zero + v_u64;
}

bool mc_getTypeInfo64(mc_getTypeInfo64_args_t args, mc_OSTType_Int64 *out, mongocrypt_status_t *status) {
    if (args.min.set != args.max.set) {
        CLIENT_ERR("Must specify both a lower and upper bound or no bounds.");
        return false;
    }

    if (!args.min.set) {
        uint64_t v_u64 = encodeInt64(args.value);
        *out = (mc_OSTType_Int64){v_u64, 0, UINT64_MAX};
        return true;
    }

    if (args.min.value >= args.max.value) {
        CLIENT_ERR("The minimum value must be less than the maximum value, got "
                   "min: %" PRId64 ", max: %" PRId64,
                   args.min.value,
                   args.max.value);
        return false;
    }

    if (args.value > args.max.value || args.value < args.min.value) {
        CLIENT_ERR("Value must be greater than or equal to the minimum value "
                   "and less than or equal to the maximum value, got "
                   "min: %" PRId64 ", max: %" PRId64 ", value: %" PRId64,
                   args.min.value,
                   args.max.value,
                   args.value);
        return false;
    }

    // Convert to unbiased uint64. Then subtract the min value.
    uint64_t v_u64 = encodeInt64(args.value);
    uint64_t min_u64 = encodeInt64(args.min.value);
    uint64_t max_u64 = encodeInt64(args.max.value);

    v_u64 -= min_u64;
    max_u64 -= min_u64;

    *out = (mc_OSTType_Int64){v_u64, 0, max_u64};
    return true;
}

#define exp10Double(x) pow(10, x)
#define SCALED_DOUBLE_BOUNDS 9007199254740992.0 // 2^53

static uint64_t subtract_int64_t(int64_t max, int64_t min) {
    BSON_ASSERT(max > min);
    // If the values have the same sign, then simple subtraction
    // will work because we know max > min.
    if ((max > 0 && min > 0) || (max < 0 && min < 0)) {
        return (uint64_t)(max - min);
    }

    // If they are opposite signs, then we can just invert
    // min to be positive and return the sum.
    uint64_t u_return = (uint64_t)max;
    u_return += (uint64_t)(~min + 1);
    return u_return;
}

static bool ceil_log2_double(uint64_t i, uint32_t *maxBitsOut, mongocrypt_status_t *status) {
    if (i == 0) {
        CLIENT_ERR("Invalid input to ceil_log2_double function. Input cannot be 0.");
        return false;
    }

    uint32_t clz = (uint32_t)_mlibCountLeadingZeros_u64(i);
    uint32_t bits;
    if ((i & (i - 1)) == 0) {
        bits = 64 - clz - 1;
    } else {
        bits = 64 - clz;
    }
    *maxBitsOut = bits;
    return true;
}

bool mc_canUsePrecisionModeDouble(double min,
                                  double max,
                                  int32_t precision,
                                  uint32_t *maxBitsOut,
                                  mongocrypt_status_t *status) {
    BSON_ASSERT_PARAM(maxBitsOut);
    BSON_ASSERT(precision >= 0);

    if (min >= max) {
        CLIENT_ERR("Invalid bounds for double range precision, min must be less than max. min: %g, max: %g", min, max);
        return false;
    }

    const double scaled_prc = exp10Double(precision);

    const double scaled_max = max * scaled_prc;
    const double scaled_min = min * scaled_prc;

    if (scaled_max != trunc(scaled_max)) {
        CLIENT_ERR("Invalid upper bound for double precision. Fractional digits must be less than the specified "
                   "precision value. max: %g",
                   max);
        return false;
    }

    if (scaled_min != trunc(scaled_min)) {
        CLIENT_ERR("Invalid lower bound for double precision. Fractional digits must be less than the specified "
                   "precision value. min: %g",
                   min);
        return false;
    }

    if (fabs(scaled_max) >= SCALED_DOUBLE_BOUNDS) {
        CLIENT_ERR(
            "Invalid upper bound for double precision. Absolute scaled value of max must be less than %g. max: %g",
            SCALED_DOUBLE_BOUNDS,
            max);
        return false;
    }

    if (fabs(scaled_min) >= SCALED_DOUBLE_BOUNDS) {
        CLIENT_ERR(
            "Invalid lower bound for double precision. Absolute scaled value of min must be less than %g. min: %g",
            SCALED_DOUBLE_BOUNDS,
            min);
        return false;
    }

    const double t_1 = scaled_max - scaled_min;
    const double t_4 = (double)UINT64_MAX - t_1;
    const double t_5 = floor(log10(t_4)) - 1;

    if ((double)precision > t_5) {
        CLIENT_ERR("Invalid value for precision. precision: %" PRId32, precision);
        return false;
    }

    const int64_t i_1 = (int64_t)(scaled_max);
    const int64_t i_2 = (int64_t)(scaled_min);

    const uint64_t range = subtract_int64_t(i_1, i_2);

    if (((uint64_t)scaled_prc) > UINT64_MAX - range) {
        CLIENT_ERR("Invalid value for min, max, and precision. The calculated domain size is too large. min: %g, max: "
                   "%g, precision: %" PRId32,
                   min,
                   max,
                   precision);
        return false;
    }

    const uint64_t i_3 = range + (uint64_t)(scaled_prc);

    if (!ceil_log2_double(i_3, maxBitsOut, status)) {
        return false;
    }

    // Integers between -2^53 and 2^53 can be exactly represented. Outside this range, doubles lose precision by a
    // multiple of 2^(n-52) where n = #bits. We disallow users from using precision mode when the bounds exceed 2^53 to
    // prevent the users from being surprised by how floating point math works.
    if (*maxBitsOut >= 53) {
        return false;
    }

    return true;
}

bool mc_getTypeInfoDouble(mc_getTypeInfoDouble_args_t args, mc_OSTType_Double *out, mongocrypt_status_t *status) {
    if (args.min.set != args.max.set || args.min.set != args.precision.set) {
        CLIENT_ERR("min, max, and precision must all be set or must all be unset");
        return false;
    }

    if (mc_isinf(args.value) || mc_isnan(args.value)) {
        CLIENT_ERR("Infinity and NaN double values are not supported.");
        return false;
    }

    if (args.min.set) {
        if (args.min.value >= args.max.value) {
            CLIENT_ERR("The minimum value must be less than the maximum value, got "
                       "min: %g, max: %g",
                       args.min.value,
                       args.max.value);
            return false;
        }

        if (args.value > args.max.value || args.value < args.min.value) {
            CLIENT_ERR("Value must be greater than or equal to the minimum value "
                       "and less than or equal to the maximum value, got "
                       "min: %g, max: %g, value: %g",
                       args.min.value,
                       args.max.value,
                       args.value);
            return false;
        }
    }

    if (args.precision.set) {
        if (args.precision.value < 0) {
            CLIENT_ERR("Precision must be non-negative, but got %" PRId32, args.precision.value);
            return false;
        }

        double scaled = exp10Double(args.precision.value);
        if (!mc_isfinite(scaled)) {
            CLIENT_ERR("Precision is too large and cannot be used to calculate the scaled range bounds");
            return false;
        }
    }

    const bool is_neg = args.value < 0.0;

    // Map negative 0 to zero so sign bit is 0.
    if (args.value == 0.0) {
        args.value = 0.0;
    }

    // When we use precision mode, we try to represent as a double value that
    // fits in [-2^63, 2^63] (i.e. is a valid int64)
    //
    // This check determines if we can represent the precision truncated value as
    // a 64-bit integer I.e. Is ((ub - lb) * 10^precision) < 64 bits.
    //
    bool use_precision_mode = false;
    uint32_t bits_range;
    if (args.precision.set) {
        use_precision_mode =
            mc_canUsePrecisionModeDouble(args.min.value, args.max.value, args.precision.value, &bits_range, status);

        if (!use_precision_mode) {
            if (!mongocrypt_status_ok(status)) {
                return false;
            }

            CLIENT_ERR("The domain of double values specified by the min, max, and precision cannot be represented in "
                       "fewer than 53 bits. min: %g, max: %g, precision: %" PRId32,
                       args.min.value,
                       args.max.value,
                       args.precision.value);
            return false;
        }

        // If we are not in range_v2, then we don't care about the error returned
        // from canUsePrecisionMode so we can reset the status.
        _mongocrypt_status_reset(status);
    }

    if (use_precision_mode) {
        // Take a number of xxxx.ppppp and truncate it xxxx.ppp if precision = 3.
        // We do not change the digits before the decimal place.
        int64_t v_prime = (int64_t)(trunc(args.value * exp10Double(args.precision.value)));
        int64_t scaled_min = (int64_t)(args.min.value * exp10Double(args.precision.value));
        int64_t v_prime2 = v_prime - scaled_min;

        BSON_ASSERT(v_prime2 < INT64_MAX && v_prime2 >= 0);

        uint64_t ret = (uint64_t)v_prime2;

        // Adjust maximum value to be the max bit range. This will be used by
        // getEdges/minCover to trim bits.
        uint64_t max_value = (UINT64_C(1) << bits_range) - 1;
        BSON_ASSERT(ret <= max_value);

        *out = (mc_OSTType_Double){ret, 0, max_value};
        return true;
    }

    // Translate double to uint64 by modifying the bit representation and copying
    // into a uint64. Double is assumed to be a IEEE 754 Binary 64.
    // It is bit-encoded as sign, exponent, and fraction:
    // s eeeeeeee ffffffffffffffffffffffffffffffffffffffffffffffffffff

    // When we translate the double into "bits", the sign bit means that the
    // negative numbers get mapped into the higher 63 bits of a 64-bit integer.
    // We want them to  map into the lower 64-bits so we invert the sign bit.
    args.value *= -1.0;

    // On Endianness, we support two sets of architectures
    // 1. Little Endian (ppc64le, x64, aarch64) - in these architectures, int64
    // and double are both 64-bits and both arranged in little endian byte order.
    // 2. Big Endian (s390x) - in these architectures, int64 and double are both
    // 64-bits and both arranged in big endian byte order.
    //
    // Therefore, since the order of bytes on each platform is consistent with
    // itself, the conversion below converts a double into correct 64-bit integer
    // that produces the same behavior across plaforms.
    uint64_t uv;
    memcpy(&uv, &args.value, sizeof(uint64_t));

    if (is_neg) {
        uint64_t new_zero = UINT64_C(1) << 63;
        BSON_ASSERT(uv <= new_zero);
        uv = new_zero - uv;
    }

    *out = (mc_OSTType_Double){.min = 0, .max = UINT64_MAX, .value = uv};

    return true;
}

#if MONGOCRYPT_HAVE_DECIMAL128_SUPPORT()
/**
 * @brief There is no shipped algorithm for creating a full 128-bit integer from
 * a Decimal128, but it's easy enough to write one of our own.
 *
 * @param dec
 * @return mlib_int128
 */
static mlib_int128 dec128_to_uint128(mc_dec128 dec) {
    // Only normal numbers
    BSON_ASSERT(mc_dec128_is_finite(dec));
    BSON_ASSERT(!mc_dec128_is_nan(dec));
    // We don't support negative numbers
    BSON_ASSERT(!mc_dec128_is_negative(dec));
    // There is no fractional part:
    BSON_ASSERT(mc_dec128_is_zero(mc_dec128_modf(dec).frac));

    mlib_int128 ret = mc_dec128_coeff(dec);

    // Scale the resulting number by a power of ten matching the exponent of the
    // Decimal128:
    int32_t exp = ((int32_t)mc_dec128_get_biased_exp(dec)) - MC_DEC128_EXPONENT_BIAS;
    // We will scale up/down based on whether it is negative:
    BSON_ASSERT(abs(exp) <= UINT8_MAX);
    mlib_int128 e1 = mlib_int128_pow10((uint8_t)abs(exp));
    if (exp < 0) {
        ret = mlib_int128_div(ret, e1);
    } else {
        ret = mlib_int128_mul(ret, e1);
    }

    return ret;
}

// (2^127 - 1) = the maximum signed 128-bit integer value, as a decimal128
#define INT_128_MAX_AS_DECIMAL mc_dec128_from_string("170141183460469231731687303715884105727")
// (2^128 - 1) = the max unsigned 128-bit integer value, as a decimal128
#define UINT_128_MAX_AS_DECIMAL mc_dec128_from_string("340282366920938463463374607431768211455")

static mlib_int128 dec128_to_int128(mc_dec128 dec) {
    BSON_ASSERT(mc_dec128_less(dec, INT_128_MAX_AS_DECIMAL));

    bool negative = false;

    if (mc_dec128_is_negative(dec)) {
        negative = true;
        dec = mc_dec128_mul(MC_DEC128(-1), dec);
    }

    mlib_int128 ret_val = dec128_to_uint128(dec);

    if (negative) {
        ret_val = mlib_int128_mul(MLIB_INT128(-1), ret_val);
    }

    return ret_val;
}

bool ceil_log2_int128(mlib_int128 i, uint32_t *maxBitsOut, mongocrypt_status_t *status) {
    if (mlib_int128_eq(i, MLIB_INT128(0))) {
        CLIENT_ERR("Invalid input to ceil_log2_int128 function. Input cannot be 0.");
        return false;
    }

    uint32_t clz = (uint32_t)_mlibCountLeadingZeros_u128(i);
    uint32_t bits;

    // if i & (i - 1) == 0
    if (mlib_int128_eq((mlib_int128_bitand(i, (mlib_int128_sub(i, MLIB_INT128(1))))), MLIB_INT128(0))) {
        bits = 128 - clz - 1;
    } else {
        bits = 128 - clz;
    }
    *maxBitsOut = bits;
    return true;
}

bool mc_canUsePrecisionModeDecimal(mc_dec128 min,
                                   mc_dec128 max,
                                   int32_t precision,
                                   uint32_t *maxBitsOut,
                                   mongocrypt_status_t *status) {
    BSON_ASSERT_PARAM(maxBitsOut);
    BSON_ASSERT(precision >= 0);

    if (!mc_dec128_is_finite(max)) {
        CLIENT_ERR("Invalid upper bound for Decimal128 precision. Max is infinite.");
        return false;
    }

    if (!mc_dec128_is_finite(min)) {
        CLIENT_ERR("Invalid lower bound for Decimal128 precision. Min is infinite.");
        return false;
    }

    if (mc_dec128_greater_equal(min, max)) {
        CLIENT_ERR("Invalid upper and lower bounds for Decimal128 precision. Min must be strictly less than max. min: "
                   "%s, max: %s",
                   mc_dec128_to_string(min).str,
                   mc_dec128_to_string(max).str);
        return false;
    }

    mc_dec128 scaled_max = mc_dec128_scale(max, precision);
    mc_dec128 scaled_min = mc_dec128_scale(min, precision);

    mc_dec128 scaled_max_trunc = mc_dec128_round_integral_ex(scaled_max, MC_DEC128_ROUND_TOWARD_ZERO, NULL);
    mc_dec128 scaled_min_trunc = mc_dec128_round_integral_ex(scaled_min, MC_DEC128_ROUND_TOWARD_ZERO, NULL);

    if (mc_dec128_not_equal(scaled_max, scaled_max_trunc)) {
        CLIENT_ERR("Invalid upper bound for Decimal128 precision. Fractional digits must be less than "
                   "the specified precision value. max: %s, precision: %" PRId32,
                   mc_dec128_to_string(max).str,
                   precision);
        return false;
    }

    if (mc_dec128_not_equal(scaled_min, scaled_min_trunc)) {
        CLIENT_ERR("Invalid lower bound for Decimal128 precision. Fractional digits must be less than "
                   "the specified precision value. min: %s, precision: %" PRId32,
                   mc_dec128_to_string(min).str,
                   precision);
        return false;
    }

    if (mc_dec128_greater(mc_dec128_abs(scaled_max), INT_128_MAX_AS_DECIMAL)) {
        CLIENT_ERR("Invalid upper bound for Decimal128 precision. Absolute scaled value must be less than "
                   "or equal to %s. max: %s",
                   mc_dec128_to_string(INT_128_MAX_AS_DECIMAL).str,
                   mc_dec128_to_string(max).str);
        return false;
    }

    if (mc_dec128_greater(mc_dec128_abs(scaled_min), INT_128_MAX_AS_DECIMAL)) {
        CLIENT_ERR("Invalid lower bound for Decimal128 precision. Absolute scaled value must be less than "
                   "or equal to %s. min: %s",
                   mc_dec128_to_string(INT_128_MAX_AS_DECIMAL).str,
                   mc_dec128_to_string(min).str);
        return false;
    }

    mc_dec128 t_1 = mc_dec128_sub(scaled_max, scaled_min);
    mc_dec128 t_4 = mc_dec128_sub(UINT_128_MAX_AS_DECIMAL, t_1);

    // t_5 = floor(log10(t_4)) - 1;
    mc_dec128 t_5 = mc_dec128_sub(mc_dec128_round_integral_ex(mc_dec128_log10(t_4), MC_DEC128_ROUND_TOWARD_ZERO, NULL),
                                  MC_DEC128(1));

    // We convert precision to a double so we can avoid warning C4146 on Windows.
    mc_dec128 prc_dec = mc_dec128_from_double((double)precision);

    if (mc_dec128_less(t_5, prc_dec)) {
        CLIENT_ERR("Invalid value for precision. precision: %" PRId32, precision);
        return false;
    }

    mlib_int128 i_1 = dec128_to_int128(scaled_max);
    mlib_int128 i_2 = dec128_to_int128(scaled_min);

    // Because we have guaranteed earlier that max is greater than min, we can
    // subtract these values and guarantee that taking their unsigned
    // representation will yield the actual range result.
    mlib_int128 range128 = mlib_int128_sub(i_1, i_2);

    if (precision > UINT8_MAX) {
        CLIENT_ERR("Invalid value for precision. Must be less than 255. precision: %" PRId32, precision);
        return false;
    }

    mlib_int128 i_3 = mlib_int128_add(range128, mlib_int128_pow10((uint8_t)precision));
    if (!ceil_log2_int128(i_3, maxBitsOut, status)) {
        return false;
    }

    if (*maxBitsOut >= 128) {
        return false;
    }

    return true;
}

bool mc_getTypeInfoDecimal128(mc_getTypeInfoDecimal128_args_t args,
                              mc_OSTType_Decimal128 *out,
                              mongocrypt_status_t *status) {
    /// Basic param checks
    if (args.min.set != args.max.set || args.min.set != args.precision.set) {
        CLIENT_ERR("min, max, and precision must all be set or must all be unset");
        return false;
    }

    if (args.precision.set) {
        if (args.precision.value < 0) {
            CLIENT_ERR("Precision must be non-negative, but got %" PRId32, args.precision.value);
            return false;
        }

        mc_dec128 scaled = mc_dec128_scale(MC_DEC128(1), args.precision.value);
        if (!mc_dec128_is_finite(scaled)) {
            CLIENT_ERR("Precision is too large and cannot be used to calculate the scaled range bounds");
            return false;
        }
    }

    // We only accept normal numbers
    if (mc_dec128_is_inf(args.value) || mc_dec128_is_nan(args.value)) {
        CLIENT_ERR("Infinity and Nan Decimal128 values are not supported.");
        return false;
    }

    // Check boundary if a range is set
    if (args.min.set) {
        // [min,max] must be valid
        if (mc_dec128_greater_equal(args.min.value, args.max.value)) {
            CLIENT_ERR("The minimum value must be less than the maximum value, got "
                       "min: %s, max: %s",
                       mc_dec128_to_string(args.min.value).str,
                       mc_dec128_to_string(args.max.value).str);
            return false;
        }

        // Value must be within [min,max)
        if (mc_dec128_greater(args.value, args.max.value) || mc_dec128_less(args.value, args.min.value)) {
            CLIENT_ERR("Value must be greater than or equal to the minimum value "
                       "and less than or equal to the maximum value, got "
                       "min: %s, max: %s, value: %s",
                       mc_dec128_to_string(args.min.value).str,
                       mc_dec128_to_string(args.max.value).str,
                       mc_dec128_to_string(args.value).str);
            return false;
        }
    }

    // Should we use precision mode?
    //
    // When we use precision mode, we try to represent as a decimal128 value that
    // fits in [-2^127, 2^127] (i.e. is a valid int128)
    //
    // This check determines if we can represent any precision-truncated value as
    // a 128-bit integer I.e. Is ((ub - lb) * 10^precision) < 128 bits.
    //
    // It is important that we determine whether a range and its precision would
    // fit, regardless of the value to be encoded, because the encoding for
    // precision-truncated-decimal128 is incompatible with the encoding of the
    // full range.
    bool use_precision_mode = false;
    // The number of bits required to hold the result (used for precision mode)
    uint32_t bits_range = 0;
    if (args.precision.set) {
        use_precision_mode =
            mc_canUsePrecisionModeDecimal(args.min.value, args.max.value, args.precision.value, &bits_range, status);

        if (!use_precision_mode) {
            if (!mongocrypt_status_ok(status)) {
                return false;
            }

            CLIENT_ERR("The domain of decimal values specified by the min, max, and precision cannot be represented in "
                       "fewer than 128 bits. min: %s, max: %s, precision: %" PRIu32,
                       mc_dec128_to_string(args.min.value).str,
                       mc_dec128_to_string(args.max.value).str,
                       args.precision.value);
            return false;
        }

        // If we are not in range_v2, then we don't care about the error returned
        // from canUsePrecisionMode so we can reset the status.
        _mongocrypt_status_reset(status);
    }

    // Constant zero
    const mlib_int128 i128_zero = MLIB_INT128(0);
    // Constant 1
    const mlib_int128 i128_one = MLIB_INT128(1);
    // Constant 10
    const mlib_int128 i128_ten = MLIB_INT128(10);
    // Constant: 2^127
    const mlib_int128 i128_2pow127 = mlib_int128_lshift(i128_one, 127);
    // ↑ Coincidentally has the same bit pattern as INT128_SMIN, but we're
    // treating it as an unsigned number here, so don't get confused!

    if (use_precision_mode) {
        BSON_ASSERT(args.precision.set);
        // Example value: 31.4159
        // Example Precision = 2

        // Shift the number up
        // Returns: 3141.9
        mc_dec128 valScaled = mc_dec128_scale(args.value, args.precision.value);

        // Round the number down
        // Returns 3141.0
        mc_dec128 valTrunc = mc_dec128_round_integral_ex(valScaled, MC_DEC128_ROUND_TOWARD_ZERO, NULL);

        // Shift the number down
        // Returns: 31.41
        mc_dec128 v_prime = mc_dec128_scale(valTrunc, -(int32_t)args.precision.value);

        // Adjust the number by the lower bound
        // Make it an integer by scaling the number
        //
        // Returns 3141.0
        mc_dec128 v_prime2 = mc_dec128_scale(mc_dec128_sub(v_prime, args.min.value), args.precision.value);
        // Round the number down again. min may have a fractional value with more
        // decimal places than the precision (e.g. .001). Subtracting min may have
        // resulted in v_prime2 with a non-zero fraction. v_prime2 is expected to
        // have no fractional value when converting to int128.
        v_prime2 = mc_dec128_round_integral_ex(v_prime2, MC_DEC128_ROUND_TOWARD_ZERO, NULL);

        BSON_ASSERT(mc_dec128_less(mc_dec128_log2(v_prime2), MC_DEC128(128)));
        BSON_ASSERT(bits_range < 128);
        // Resulting OST maximum
        mlib_int128 ost_max = mlib_int128_sub(mlib_int128_pow2((uint8_t)bits_range), i128_one);

        // Now we need to get the Decimal128 out as a 128-bit integer
        // But Decimal128 does not support conversion to Int128.
        //
        // If we think the Decimal128 fits in the range, based on the maximum
        // value, we try to convert to int64 directly.
        if (bits_range < 64) {
            // Try conversion to int64, it may fail but since it is easy we try
            // this first.
            mc_dec128_flagset flags = {0};
            int64_t as64 = mc_dec128_to_int64_ex(v_prime2, &flags);
            if (flags.bits == 0) {
                // No error. It fits
                *out = (mc_OSTType_Decimal128){
                    .value = MLIB_INT128_CAST(as64),
                    .min = i128_zero,
                    .max = ost_max,
                };
                return true;
            } else {
                // Conversion failure to 64-bit. Possible overflow, imprecision,
                // etc. Fallback to slower dec128_to_int128
            }
        }

        mlib_int128 u_ret = dec128_to_int128(v_prime2);

        *out = (mc_OSTType_Decimal128){
            .value = u_ret,
            .min = i128_zero,
            .max = ost_max,
        };

        return true;
    }

    // The coefficient of the number, without exponent/sign
    const mlib_int128 coeff = mc_dec128_coeff(args.value);

    if (mlib_int128_eq(coeff, i128_zero)) {
        // If the coefficient is zero, the result is encoded as the midpoint
        // between zero and 2^128-1
        *out = (mc_OSTType_Decimal128){
            .value = i128_2pow127,
            .min = i128_zero,
            .max = MLIB_INT128_UMAX,
        };
        return true;
    }

    // Coefficient is an unsigned value. We'll later scale our answer based on
    // the sign of the actual Decimal128
    const bool isNegative = mc_dec128_is_negative(args.value);

    // cMax = 10^34 - 1 (The largest integer representable in Decimal128)
    const mlib_int128 cMax = mlib_int128_sub(mlib_int128_pow10(34), MLIB_INT128_CAST(1));
    const mlib_int128 cMax_div_ten = mlib_int128_div(cMax, i128_ten);

    // The biased exponent from the decimal number. The paper refers to the
    // expression (e - e_min), which is the value of the biased exponent.
    const uint32_t exp_biased = mc_dec128_get_biased_exp(args.value);

    // ρ (rho) is the greatest integer such that: coeff×10^ρ <= cMax
    unsigned rho = 0;
    // Keep track of the subexpression coeff×10^ρ rather than recalculating it
    // time.
    // Initially: (ρ = 0) -> (10^ρ = 1) -> (coeff×10^ρ = coeff×1 = coeff):
    mlib_int128 coeff_scaled = coeff;
    // Calculate ρ: This could be done using a log10 with a division, but that
    // is far more work than just a few multiplications.
    // While: coeff×ten^ρ < cMax/10:
    while (mlib_int128_ucmp(coeff_scaled, cMax_div_ten) < 0) {
        // Increase rho until we pass cMax/10
        rho++;
        // Scale our computed subexpression rather than fully recomputing it
        coeff_scaled = mlib_int128_mul(coeff_scaled, i128_ten);
    }

    // No multiplication by 10 should ever send us from N < cMax/10 to N > cMax
    BSON_ASSERT(mlib_int128_ucmp(coeff_scaled, cMax) <= 0);

    mlib_int128 result;
    if (rho <= exp_biased) {
        // ρ is less-than/equal to the exponent with bias.

        // Diff between the biased exponent and ρ.
        // Value in paper is spelled "e - e_min - ρ"
        const uint32_t exp_diff = exp_biased - (uint32_t)rho;
        // cMax * (exp_diff)
        const mlib_int128 cmax_scaled = mlib_int128_mul(cMax, MLIB_INT128_CAST(exp_diff));
        // coeff * 10^rho * cMax * (exp_biased - rho)
        result = mlib_int128_add(coeff_scaled, cmax_scaled);
    } else {
        const mlib_int128 biased_scale = mlib_int128_pow10((uint8_t)exp_biased);
        result = mlib_int128_mul(biased_scale, coeff);
    }

    // Always add 2^127:
    result = mlib_int128_add(result, i128_2pow127);

    if (isNegative) {
        // We calculated the value of the positive coefficient, but the decimal is
        // negative. That's okay: Just flip the sign of the encoded result:
        result = mlib_int128_negate(result);
    }

    *out = (mc_OSTType_Decimal128){
        .value = result,
        .min = i128_zero,
        .max = MLIB_INT128_UMAX,
    };

    return true;
}

#endif // defined MONGOCRYPT_HAVE_DECIMAL128_SUPPORT

const int64_t mc_FLERangeSparsityDefault = 2;
static const int32_t mc_FLERangeTrimFactorDefault = 6;

int32_t trimFactorDefault(size_t maxlen, mc_optional_int32_t trimFactor) {
    if (trimFactor.set) {
        return trimFactor.value;
    }

    if (mc_cmp_greater_su(mc_FLERangeTrimFactorDefault, maxlen - 1)) {
        return (int32_t)(maxlen - 1);
    } else {
        return mc_FLERangeTrimFactorDefault;
    }
}
