133 lines
3.8 KiB
Zig
133 lines
3.8 KiB
Zig
const std = @import("../../index.zig");
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const debug = std.debug;
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const math = std.math;
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const cmath = math.complex;
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const Complex = cmath.Complex;
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const ldexp_cexp = @import("ldexp.zig").ldexp_cexp;
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pub fn exp(z: var) @typeOf(z) {
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const T = @typeOf(z.re);
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return switch (T) {
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f32 => exp32(z),
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f64 => exp64(z),
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else => @compileError("exp not implemented for " ++ @typeName(z)),
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};
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}
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fn exp32(z: Complex(f32)) Complex(f32) {
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const exp_overflow = 0x42b17218; // max_exp * ln2 ~= 88.72283955
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const cexp_overflow = 0x43400074; // (max_exp - min_denom_exp) * ln2
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const x = z.re;
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const y = z.im;
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const hy = @bitCast(u32, y) & 0x7fffffff;
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// cexp(x + i0) = exp(x) + i0
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if (hy == 0) {
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return Complex(f32).new(math.exp(x), y);
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}
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const hx = @bitCast(u32, x);
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// cexp(0 + iy) = cos(y) + isin(y)
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if ((hx & 0x7fffffff) == 0) {
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return Complex(f32).new(math.cos(y), math.sin(y));
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}
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if (hy >= 0x7f800000) {
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// cexp(finite|nan +- i inf|nan) = nan + i nan
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if ((hx & 0x7fffffff) != 0x7f800000) {
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return Complex(f32).new(y - y, y - y);
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} // cexp(-inf +- i inf|nan) = 0 + i0
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else if (hx & 0x80000000 != 0) {
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return Complex(f32).new(0, 0);
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} // cexp(+inf +- i inf|nan) = inf + i nan
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else {
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return Complex(f32).new(x, y - y);
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}
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}
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// 88.7 <= x <= 192 so must scale
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if (hx >= exp_overflow and hx <= cexp_overflow) {
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return ldexp_cexp(z, 0);
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} // - x < exp_overflow => exp(x) won't overflow (common)
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// - x > cexp_overflow, so exp(x) * s overflows for s > 0
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// - x = +-inf
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// - x = nan
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else {
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const exp_x = math.exp(x);
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return Complex(f32).new(exp_x * math.cos(y), exp_x * math.sin(y));
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}
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}
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fn exp64(z: Complex(f64)) Complex(f64) {
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const exp_overflow = 0x40862e42; // high bits of max_exp * ln2 ~= 710
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const cexp_overflow = 0x4096b8e4; // (max_exp - min_denorm_exp) * ln2
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const x = z.re;
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const y = z.im;
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const fy = @bitCast(u64, y);
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const hy = u32(fy >> 32) & 0x7fffffff;
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const ly = @truncate(u32, fy);
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// cexp(x + i0) = exp(x) + i0
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if (hy | ly == 0) {
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return Complex(f64).new(math.exp(x), y);
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}
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const fx = @bitCast(u64, x);
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const hx = u32(fx >> 32);
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const lx = @truncate(u32, fx);
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// cexp(0 + iy) = cos(y) + isin(y)
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if ((hx & 0x7fffffff) | lx == 0) {
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return Complex(f64).new(math.cos(y), math.sin(y));
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}
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if (hy >= 0x7ff00000) {
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// cexp(finite|nan +- i inf|nan) = nan + i nan
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if (lx != 0 or (hx & 0x7fffffff) != 0x7ff00000) {
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return Complex(f64).new(y - y, y - y);
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} // cexp(-inf +- i inf|nan) = 0 + i0
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else if (hx & 0x80000000 != 0) {
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return Complex(f64).new(0, 0);
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} // cexp(+inf +- i inf|nan) = inf + i nan
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else {
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return Complex(f64).new(x, y - y);
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}
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}
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// 709.7 <= x <= 1454.3 so must scale
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if (hx >= exp_overflow and hx <= cexp_overflow) {
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const r = ldexp_cexp(z, 0);
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return r.*;
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} // - x < exp_overflow => exp(x) won't overflow (common)
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// - x > cexp_overflow, so exp(x) * s overflows for s > 0
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// - x = +-inf
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// - x = nan
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else {
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const exp_x = math.exp(x);
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return Complex(f64).new(exp_x * math.cos(y), exp_x * math.sin(y));
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}
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}
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const epsilon = 0.0001;
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test "complex.cexp32" {
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const a = Complex(f32).new(5, 3);
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const c = exp(a);
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debug.assert(math.approxEq(f32, c.re, -146.927917, epsilon));
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debug.assert(math.approxEq(f32, c.im, 20.944065, epsilon));
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}
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test "complex.cexp64" {
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const a = Complex(f32).new(5, 3);
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const c = exp(a);
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debug.assert(math.approxEq(f64, c.re, -146.927917, epsilon));
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debug.assert(math.approxEq(f64, c.im, 20.944065, epsilon));
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}
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