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diff --git a/subprojects/exess/src/bigint.h b/subprojects/exess/src/bigint.h
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+/*
+  Copyright 2019-2021 David Robillard <d@drobilla.net>
+
+  Permission to use, copy, modify, and/or distribute this software for any
+  purpose with or without fee is hereby granted, provided that the above
+  copyright notice and this permission notice appear in all copies.
+
+  THIS SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+  WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+  MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+  ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+  WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+  ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+  OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+
+#ifndef EXESS_BIGINT_H
+#define EXESS_BIGINT_H
+
+#include "attributes.h"
+
+#include <stddef.h>
+#include <stdint.h>
+#include <stdio.h>
+
+typedef uint32_t Bigit;
+
+/* We need enough precision for any double, the "largest" of which (using
+   absolute exponents) is the smallest subnormal ~= 5e-324.  This is 1076 bits
+   long, but we need a bit more space for arithmetic.  This is absurd, but such
+   is decimal.  These are only used on the stack so it doesn't hurt too much.
+*/
+
+#define BIGINT_MAX_SIGNIFICANT_BITS 1280u
+#define BIGINT_BIGIT_BITS 32u
+#define BIGINT_MAX_BIGITS (BIGINT_MAX_SIGNIFICANT_BITS / BIGINT_BIGIT_BITS)
+
+typedef struct {
+  Bigit    bigits[BIGINT_MAX_BIGITS];
+  unsigned n_bigits;
+} ExessBigint;
+
+void
+exess_bigint_zero(ExessBigint* num);
+
+size_t
+exess_bigint_print_hex(FILE* stream, const ExessBigint* num);
+
+void
+exess_bigint_clamp(ExessBigint* num);
+
+void
+exess_bigint_shift_left(ExessBigint* num, unsigned amount);
+
+void
+exess_bigint_set(ExessBigint* num, const ExessBigint* value);
+
+void
+exess_bigint_set_u32(ExessBigint* num, uint32_t value);
+
+void
+exess_bigint_set_u64(ExessBigint* num, uint64_t value);
+
+void
+exess_bigint_set_pow10(ExessBigint* num, unsigned exponent);
+
+void
+exess_bigint_set_decimal_string(ExessBigint* num, const char* str);
+
+void
+exess_bigint_set_hex_string(ExessBigint* num, const char* str);
+
+void
+exess_bigint_multiply_u32(ExessBigint* num, uint32_t factor);
+
+void
+exess_bigint_multiply_u64(ExessBigint* num, uint64_t factor);
+
+void
+exess_bigint_multiply_pow10(ExessBigint* num, unsigned exponent);
+
+EXESS_I_PURE_FUNC
+int
+exess_bigint_compare(const ExessBigint* lhs, const ExessBigint* rhs);
+
+void
+exess_bigint_add_u32(ExessBigint* lhs, uint32_t rhs);
+
+void
+exess_bigint_add(ExessBigint* lhs, const ExessBigint* rhs);
+
+void
+exess_bigint_subtract(ExessBigint* lhs, const ExessBigint* rhs);
+
+EXESS_I_PURE_FUNC
+Bigit
+exess_bigint_left_shifted_bigit(const ExessBigint* num,
+                                unsigned           amount,
+                                unsigned           index);
+
+/// Faster implementation of exess_bigint_subtract(lhs, rhs << amount)
+void
+exess_bigint_subtract_left_shifted(ExessBigint*       lhs,
+                                   const ExessBigint* rhs,
+                                   unsigned           amount);
+
+/// Faster implementation of exess_bigint_compare(l + p, c)
+EXESS_I_PURE_FUNC
+int
+exess_bigint_plus_compare(const ExessBigint* l,
+                          const ExessBigint* p,
+                          const ExessBigint* c);
+
+/// Divide and set `lhs` to modulo
+uint32_t
+exess_bigint_divmod(ExessBigint* lhs, const ExessBigint* rhs);
+
+#endif // EXESS_BIGINT_H