maths.h

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#ifndef MATH_H
#define MATH_H
 
#include <stdint.h>
#include "globals.h"
#include "bit_shifts.h"
 
#ifdef USE_LIBDIVIDE
// We use pre-computed constant parameters with libdivide where possible. 
// Using predefined constants saves flash and RAM (.bss) versus calling the 
// libdivide generator functions (E.g. libdivide_s32_gen)
// 32-bit constants generated here: https://godbolt.org/z/vP8Kfejo9
#include "src/libdivide/libdivide.h"
#include "src/libdivide/constant_fast_div.h"
#endif
 
uint8_t random1to100(void);
 
#define DIV_ROUND_DOWN -1
 
#define DIV_ROUND_UP 1
 
#define DIV_ROUND_NEAREST 0
 
#define DIV_ROUND_BEHAVIOR DIV_ROUND_NEAREST
// (Unit tests expect DIV_ROUND_NEAREST behavior)
 
#define DIV_ROUND_CORRECT(d, t) ((t)(((d)>>1U)+(t)DIV_ROUND_BEHAVIOR))
 
#define DIV_ROUND_CLOSEST(n, d, t) ( \
    (((n) < (t)(0)) ^ ((d) < (t)(0))) ? \
        ((t)((n) - DIV_ROUND_CORRECT(d, t))/(t)(d)) : \
        ((t)((n) + DIV_ROUND_CORRECT(d, t))/(t)(d)))
 
#define UDIV_ROUND_CLOSEST(n, d, t) ((t)((n) + DIV_ROUND_CORRECT(d, t))/(t)(d))
 
 
#define IS_INTEGER(d) ((d) == (int32_t)(d))
 
static inline uint16_t div100(uint16_t n) {
    // As of avr-gcc 5.4.0, the compiler will optimize this to a multiply/shift
    // (unlike the signed integer overload, where __divmodhi4 is still called
    // see https://godbolt.org/z/c5bs5noT1)
    return UDIV_ROUND_CLOSEST(n, UINT16_C(100), uint16_t);
}
 
static inline int16_t div100(int16_t n) {
#ifdef USE_LIBDIVIDE
    // Try faster unsigned path first
    if (n>0) {
        return div100((uint16_t)n);
    }
    // Negative values here, so adjust pre-division to get same
    // behavior as roundf(float)
    return libdivide::libdivide_s16_do_raw(n - DIV_ROUND_CORRECT(UINT16_C(100), uint16_t), S16_MAGIC(100), S16_MORE(100));
#else
    return DIV_ROUND_CLOSEST(n, UINT16_C(100), int16_t);
#endif
}
 
static inline uint32_t div100(uint32_t n) {
#ifdef USE_LIBDIVIDE
    if (n<=(uint32_t)UINT16_MAX) {
        return div100((uint16_t)n);
    }
    return libdivide::libdivide_u32_do_raw(n + DIV_ROUND_CORRECT(UINT32_C(100), uint32_t), 2748779070L, 6);
#else
    return UDIV_ROUND_CLOSEST(n, UINT32_C(100), uint32_t);
#endif
}
 
#if defined(__arm__)
static inline int div100(int n) {
    return DIV_ROUND_CLOSEST(n, 100U, int);
}
#else
static inline int32_t div100(int32_t n) {
#ifdef USE_LIBDIVIDE    
    if (n<=INT16_MAX && n>=INT16_MIN) {
        return div100((int16_t)n);            
    }
    return libdivide::libdivide_s32_do_raw(n + (DIV_ROUND_CORRECT(UINT16_C(100), uint32_t) * (n<0 ? -1 : 1)), 1374389535L, 5);
#else
    return DIV_ROUND_CLOSEST(n, INT32_C(100), int32_t);
#endif
}
#endif
 
static inline uint32_t div360(uint32_t n) {
#ifdef USE_LIBDIVIDE
    return libdivide::libdivide_u32_do_raw(n + DIV_ROUND_CORRECT(UINT32_C(360), uint32_t), 1813430637L, 72);
#else
    return (uint32_t)UDIV_ROUND_CLOSEST(n, UINT32_C(360), uint32_t);
#endif
}
 
static inline uint32_t percentage(uint8_t percent, uint32_t value) 
{
    return (uint32_t)div100((uint32_t)value * (uint32_t)percent);
}
 
 
static inline uint16_t halfPercentage(uint8_t percent, uint16_t value) {
    uint32_t x200 = (uint32_t)percent * (uint32_t)value;
#ifdef USE_LIBDIVIDE    
    return (uint16_t)libdivide::libdivide_u32_do_raw(x200 + DIV_ROUND_CORRECT(UINT32_C(200), uint32_t), 2748779070L, 7);
#else
    return (uint16_t)UDIV_ROUND_CLOSEST(x200, UINT16_C(200), uint32_t);
#endif
}
 
static inline int16_t nudge(int16_t min, int16_t max, int16_t value, int16_t nudgeAmount)
{
    if (value<min) { return value + nudgeAmount; }
    if (value>max) { return value - nudgeAmount; }
    return value;
}
 
#if defined(CORE_AVR) || defined(ARDUINO_ARCH_AVR)
 
static inline bool udiv_is16bit_result(uint32_t dividend, uint16_t divisor) {
  return divisor>(uint16_t)(dividend>>16U);
}
 
#endif
static inline uint16_t udiv_32_16 (uint32_t dividend, uint16_t divisor)
{
#if defined(CORE_AVR) || defined(ARDUINO_ARCH_AVR)
 
    if (divisor==0U || !udiv_is16bit_result(dividend, divisor)) { return UINT16_MAX; }
 
    #define INDEX_REG "r16"
 
    asm(
        "    ldi " INDEX_REG ", 16 ; bits = 16\n\t"
        "0:\n\t"
        "    lsl  %A0     ; shift\n\t"
        "    rol  %B0     ;  rem:quot\n\t"
        "    rol  %C0     ;   left\n\t"
        "    rol  %D0     ;    by 1\n\t"
        "    brcs 1f     ; if carry out, rem > divisor\n\t"
        "    cp   %C0, %A1 ; is rem less\n\t"
        "    cpc  %D0, %B1 ;  than divisor ?\n\t"
        "    brcs 2f     ; yes, when carry out\n\t"
        "1:\n\t"
        "    sub  %C0, %A1 ; compute\n\t"
        "    sbc  %D0, %B1 ;  rem -= divisor\n\t"
        "    ori  %A0, 1  ; record quotient bit as 1\n\t"
        "2:\n\t"
        "    dec  " INDEX_REG "     ; bits--\n\t"
        "    brne 0b     ; until bits == 0"
        : "=d" (dividend) 
        : "d" (divisor) , "0" (dividend) 
        : INDEX_REG
    );
 
    // Lower word contains the quotient, upper word contains the remainder.
    return dividend & 0xFFFFU;
#else
    // The non-AVR platforms are all fast enough (or have built in hardware dividers)
    // so just fall back to regular 32-bit division.
    return dividend / divisor;
#endif
}
 
 
static inline uint16_t udiv_32_16_closest(uint32_t dividend, uint16_t divisor)
{
#if defined(CORE_AVR) || defined(ARDUINO_ARCH_AVR)
    dividend = dividend + (uint32_t)(DIV_ROUND_CORRECT(divisor, uint16_t));
    return udiv_32_16(dividend, divisor);
#else
    return (uint16_t)UDIV_ROUND_CLOSEST(dividend, (uint32_t)divisor, uint32_t);
#endif
}
 
template<class T>
constexpr const T& clamp(const T& v, const T& lo, const T& hi){
    return v<lo ? lo : hi<v ? hi : v;
}
 
 
template <typename T, typename TPrime>
static inline T LOW_PASS_FILTER_8BIT(T input, uint8_t alpha, T prior) {
  // Intermediate steps are for MISRA compliance
  // Equivalent to: (input * (256 - alpha) + (prior * alpha)) >> 8
  static constexpr T ALPHA_MAX = (T)256;
  T inv_alpha = ALPHA_MAX - (T)alpha;
  TPrime prior_alpha = (prior * (TPrime)alpha);
  TPrime preshift = (input * (TPrime)inv_alpha) + prior_alpha;
  return (T)(preshift / ALPHA_MAX); // Division should resolve to a shift & avoids a MISRA violation
}
 
 
static inline uint16_t LOW_PASS_FILTER(uint16_t input, uint8_t alpha, uint16_t prior) {
    return LOW_PASS_FILTER_8BIT<uint16_t, uint32_t>(input, alpha, prior);
}
 
static inline int16_t LOW_PASS_FILTER(int16_t input, uint8_t alpha, int16_t prior) {
    return LOW_PASS_FILTER_8BIT<int16_t, int32_t>(input, alpha, prior);
}
 
#endif