trig8.h

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#ifndef __INC_LIB8TION_TRIG_H
#define __INC_LIB8TION_TRIG_H
 
 
 
 
#if defined(__AVR__)
 
#define sin16 sin16_avr
 
LIB8STATIC int16_t sin16_avr(uint16_t theta) {
    static const uint8_t data[] = {
        0,           0,           49, 0, 6393 % 256,  6393 / 256,  48, 0,
        12539 % 256, 12539 / 256, 44, 0, 18204 % 256, 18204 / 256, 38, 0,
        23170 % 256, 23170 / 256, 31, 0, 27245 % 256, 27245 / 256, 23, 0,
        30273 % 256, 30273 / 256, 14, 0, 32137 % 256, 32137 / 256, 4 /*,0*/};
 
    uint16_t offset = (theta & 0x3FFF);
 
    // AVR doesn't have a multi-bit shift instruction,
    // so if we say "offset >>= 3", gcc makes a tiny loop.
    // Inserting empty volatile statements between each
    // bit shift forces gcc to unroll the loop.
    offset >>= 1; // 0..8191
    asm volatile("");
    offset >>= 1; // 0..4095
    asm volatile("");
    offset >>= 1; // 0..2047
 
    if (theta & 0x4000)
        offset = 2047 - offset;
 
    uint8_t sectionX4;
    sectionX4 = offset / 256;
    sectionX4 *= 4;
 
    uint8_t m;
 
    union {
        uint16_t b;
        struct {
            uint8_t blo;
            uint8_t bhi;
        };
    } u;
 
    // in effect u.b = blo + (256 * bhi);
    u.blo = data[sectionX4];
    u.bhi = data[sectionX4 + 1];
    m = data[sectionX4 + 2];
 
    uint8_t secoffset8 = (uint8_t)(offset) / 2;
 
    uint16_t mx = m * secoffset8;
 
    int16_t y = mx + u.b;
    if (theta & 0x8000)
        y = -y;
 
    return y;
}
 
#else
 
#define sin16 sin16_C
 
LIB8STATIC int16_t sin16_C(uint16_t theta) {
    static const uint16_t base[] = {0,     6393,  12539, 18204,
                                    23170, 27245, 30273, 32137};
    static const uint8_t slope[] = {49, 48, 44, 38, 31, 23, 14, 4};
 
    uint16_t offset = (theta & 0x3FFF) >> 3; // 0..2047
    if (theta & 0x4000)
        offset = 2047 - offset;
 
    uint8_t section = offset / 256; // 0..7
    uint16_t b = base[section];
    uint8_t m = slope[section];
 
    uint8_t secoffset8 = (uint8_t)(offset) / 2;
 
    uint16_t mx = m * secoffset8;
    int16_t y = mx + b;
 
    if (theta & 0x8000)
        y = -y;
 
    return y;
}
 
#endif
 
LIB8STATIC int16_t cos16(uint16_t theta) { return sin16(theta + 16384); }
 
// sin8() and cos8()
// Fast 8-bit approximations of sin(x) & cos(x).
 
const uint8_t b_m16_interleave[] = {0, 49, 49, 41, 90, 27, 117, 10};
 
#if defined(__AVR__) && !defined(LIB8_ATTINY)
#define sin8 sin8_avr
 
LIB8STATIC uint8_t sin8_avr(uint8_t theta) {
    uint8_t offset = theta;
 
    asm volatile("sbrc %[theta],6         \n\t"
                 "com  %[offset]           \n\t"
                 : [theta] "+r"(theta), [offset] "+r"(offset));
 
    offset &= 0x3F; // 0..63
 
    uint8_t secoffset = offset & 0x0F; // 0..15
    if (theta & 0x40)
        ++secoffset;
 
    uint8_t m16;
    uint8_t b;
 
    uint8_t section = offset >> 4; // 0..3
    uint8_t s2 = section * 2;
 
    const uint8_t *p = b_m16_interleave;
    p += s2;
    b = *p;
    ++p;
    m16 = *p;
 
    uint8_t mx;
    uint8_t xr1;
    asm volatile("mul %[m16],%[secoffset]   \n\t"
                 "mov %[mx],r0              \n\t"
                 "mov %[xr1],r1             \n\t"
                 "eor  r1, r1               \n\t"
                 "swap %[mx]                \n\t"
                 "andi %[mx],0x0F           \n\t"
                 "swap %[xr1]               \n\t"
                 "andi %[xr1], 0xF0         \n\t"
                 "or   %[mx], %[xr1]        \n\t"
                 : [mx] "=d"(mx), [xr1] "=d"(xr1)
                 : [m16] "d"(m16), [secoffset] "d"(secoffset));
 
    int8_t y = mx + b;
    if (theta & 0x80)
        y = -y;
 
    y += 128;
 
    return y;
}
 
#else
 
#define sin8 sin8_C
 
LIB8STATIC uint8_t sin8_C(uint8_t theta) {
    uint8_t offset = theta;
    if (theta & 0x40) {
        offset = (uint8_t)255 - offset;
    }
    offset &= 0x3F; // 0..63
 
    uint8_t secoffset = offset & 0x0F; // 0..15
    if (theta & 0x40)
        ++secoffset;
 
    uint8_t section = offset >> 4; // 0..3
    uint8_t s2 = section * 2;
    const uint8_t *p = b_m16_interleave;
    p += s2;
    uint8_t b = *p;
    ++p;
    uint8_t m16 = *p;
 
    uint8_t mx = (m16 * secoffset) >> 4;
 
    int8_t y = mx + b;
    if (theta & 0x80)
        y = -y;
 
    y += 128;
 
    return y;
}
 
#endif
 
LIB8STATIC uint8_t cos8(uint8_t theta) { return sin8(theta + 64); }
 
 
#endif