PER Utility Functions

Header-only helpers for embedded C. All macros are type-safe (_Generic dispatched) and force-inlined when applicable. Include them directly:

#include "common/utils/max.h"
#include "common/utils/clamp.h"
// ...

max.h / min.h

Inline functions to compute the maximum or minimum of 2, 3, or 4 ints or floats.

int a = 5, b = 3, c = 10, d = 7;
int hi = MAXOF(a, b);        // 5
hi = MAXOF(a, b, c);         // 10
hi = MAXOF(a, b, c, d);      // 10
 
float x = 1.5f, y = 2.3f, z = 0.8f;
float lo = MINOF(x, y);      // 1.5
lo = MINOF(x, y, z);         // 0.8

abs.h

ABS(x) returns the absolute value of an int or float.

int   ai = ABS(-7);     // 7
float af = ABS(-1.25f); // 1.25

clamp.h

CLAMP(input, lower, upper) saturates a value into [lower, upper]. Works on int, unsigned int, long, unsigned long, and float.

int duty       = CLAMP(raw_duty, 0, 100);            // 0..100 %
float throttle = CLAMP(pedal_pos, 0.0f, 1.0f);       // 0..1

rescale.h

RESCALE(input, in_min, in_max, out_min, out_max) linearly maps a value from one range to another. Returns out_min if the input range is zero (no div-by-zero).

// 12-bit ADC counts -> 0..3.3 V
float v = RESCALE((float)adc_counts, 0.0f, 4095.0f, 0.0f, 3.3f);
 
// Steering sensor counts -> degrees
int deg = RESCALE(counts, 0, 1023, -180, 180);

countof.h

countof(array) returns the number of elements in a stack/global array. Passing a pointer is rejected at compile time.

int rails[] = { RAIL_24V, RAIL_5V, RAIL_3V3 };
for (size_t i = 0; i < countof(rails); ++i) {
    enable_rail(rails[i]);
}

units.h

Tiny typed wrappers around physical units. Each unit is a struct holding a single float, so they cost nothing at runtime but stop you from accidentally mixing, e.g., feet with meters.

Available unit families: temperature (C/F), distance (m/cm/mm/in/ft/mi), time (ms/s/min/hr/day), angle (rad/deg), mass (g/kg/lb), pressure (Pa/psi/bar), velocity (mps/kph/mph).

celsius_t board_temp = { .value = 42.0f };
fahrenheit_t f       = fahrenheit_from(board_temp);   // 107.6 F
 
degrees_t   steer_deg = { .value = 90.0f };
radians_t   steer_rad = radians_from(steer_deg);      // pi/2
 
// _Generic shorthand: the right converter is picked from the input type.
meters_t  d = meters_from((feet_t){ .value = 10.0f }); // 3.048 m
seconds_t t = seconds_from((minutes_t){ .value = 5.0f }); // 300 s

linear_algebra.h

Float-only vector3_t / matrix3x3_t / euler_angles_t plus the basic operations needed for IMU/orientation work: magnitude, normalize, matrix-vector and matrix-matrix multiply, and a Tait-Bryan ZYX Euler-to-rotation-matrix helper.

vector3_t accel = { 0.1f, 0.2f, 9.7f };
float mag       = vector3_magnitude(accel);          // ~9.71
vector3_t unit  = vector3_normalize(accel);
 
euler_angles_t a = { .roll = 0.0f, .pitch = 0.1f, .yaw = 0.2f };
matrix3x3_t R   = tait_bryan(a);
vector3_t world = matrix_multiply_vector3(&R, &accel);