Commit fd680ba5fbe99dde71b6ec28ecae1cddf4fed71b | zig

author	mihael <hi@mihaelm.com> 2026-03-15 23:13:24+01:00
committer	mihael <hi@mihaelm.com> 2026-03-17 23:33:10+01:00
log	fd680ba5fbe99dde71b6ec28ecae1cddf4fed71b
tree	a5b1fc432fb8ae0c8e0b4718070bc297ff46ba16
parent	4cad6f5372f6f17e249c24fba4d23466fa853fc0
signature	Signed by SSH key SHA256:aoFoShdYLdrqMichqKXSSieTKUfACUIDJHsKc4V2tQg

`libzigc`: Implement `tanh`

The changes were tested by running following commands:

```
$ ./build/stage3/bin/zig build -p stage4 -Denable-llvm -Dno-lib

$ stage4/bin/zig build test-libc -Dlibc-test-path=<LIBC-TEST-PATH> -Dtest-filter=tanh -fqemu -fwasmtime --summary line
Build Summary: 1289/1289 steps succeeded
```

4 files changed, 5 insertions(+), 47 deletions(-)

lib
- c
  - math.zig
- libc
  - musl
    src
    math
    tanh.c
src
- libs
  - musl.zig
  - wasi_libc.zig

lib/c/math.zig+5

...	@@ -63,6 +63,7 @@ comptime {	...	@@ -63,6 +63,7 @@ comptime {
63	symbol(&pow, "pow");	63	symbol(&pow, "pow");
64	symbol(&pow10, "pow10");	64	symbol(&pow10, "pow10");
65	symbol(&pow10f, "pow10f");	65	symbol(&pow10f, "pow10f");
		66	symbol(&tanh, "tanh");
66	}	67	}
67		68
68	if (builtin.target.isMuslLibC()) {	69	if (builtin.target.isMuslLibC()) {
...	@@ -338,3 +339,7 @@ test "rint" {	...	@@ -338,3 +339,7 @@ test "rint" {
338	try expectEqual(@as(f64, 2.0), rint(2.5));	339	try expectEqual(@as(f64, 2.0), rint(2.5));
339	try expectEqual(@as(f64, 4.0), rint(3.5));	340	try expectEqual(@as(f64, 4.0), rint(3.5));
340	}	341	}
		342
		343	fn tanh(x: f64) callconv(.c) f64 {
		344	return math.tanh(x);
		345	}

lib/libc/musl/src/math/tanh.c deleted-45

...	@@ -1,45 +0,0 @@
1	#include "libm.h"
2
3	/* tanh(x) = (exp(x) - exp(-x))/(exp(x) + exp(-x))
4	* = (exp(2x) - 1)/(exp(2x) - 1 + 2)
5	* = (1 - exp(-2x))/(exp(-2x) - 1 + 2)
6	*/
7	double tanh(double x)
8	{
9	union {double f; uint64_t i;} u = {.f = x};
10	uint32_t w;
11	int sign;
12	double_t t;
13
14	/* x = \|x\| */
15	sign = u.i >> 63;
16	u.i &= (uint64_t)-1/2;
17	x = u.f;
18	w = u.i >> 32;
19
20	if (w > 0x3fe193ea) {
21	/* \|x\| > log(3)/2 ~= 0.5493 or nan */
22	if (w > 0x40340000) {
23	/* \|x\| > 20 or nan */
24	/* note: this branch avoids raising overflow */
25	t = 1 - 0/x;
26	} else {
27	t = expm1(2*x);
28	t = 1 - 2/(t+2);
29	}
30	} else if (w > 0x3fd058ae) {
31	/* \|x\| > log(5/3)/2 ~= 0.2554 */
32	t = expm1(2*x);
33	t = t/(t+2);
34	} else if (w >= 0x00100000) {
35	/* \|x\| >= 0x1p-1022, up to 2ulp error in [0.1,0.2554] */
36	t = expm1(-2*x);
37	t = -t/(t+2);
38	} else {
39	/* \|x\| is subnormal */
40	/* note: the branch above would not raise underflow in [0x1p-1023,0x1p-1022) */
41	FORCE_EVAL((float)x);
42	t = x;
43	}
44	return sign ? -t : t;
45	}

src/libs/musl.zig-1

...	@@ -1003,7 +1003,6 @@ const src_files = [_][]const u8{	...	@@ -1003,7 +1003,6 @@ const src_files = [_][]const u8{
1003	"musl/src/math/sinl.c",	1003	"musl/src/math/sinl.c",
1004	"musl/src/math/__tan.c",	1004	"musl/src/math/__tan.c",
1005	"musl/src/math/__tandf.c",	1005	"musl/src/math/__tandf.c",
1006	"musl/src/math/tanh.c",
1007	"musl/src/math/tanhf.c",	1006	"musl/src/math/tanhf.c",
1008	"musl/src/math/tanhl.c",	1007	"musl/src/math/tanhl.c",
1009	"musl/src/math/__tanl.c",	1008	"musl/src/math/__tanl.c",

src/libs/wasi_libc.zig-1

...	@@ -793,7 +793,6 @@ const libc_top_half_src_files = [_][]const u8{	...	@@ -793,7 +793,6 @@ const libc_top_half_src_files = [_][]const u8{
793	"musl/src/math/sinl.c",	793	"musl/src/math/sinl.c",
794	"musl/src/math/__tan.c",	794	"musl/src/math/__tan.c",
795	"musl/src/math/__tandf.c",	795	"musl/src/math/__tandf.c",
796	"musl/src/math/tanh.c",
797	"musl/src/math/tanhf.c",	796	"musl/src/math/tanhf.c",
798	"musl/src/math/tanhl.c",	797	"musl/src/math/tanhl.c",
799	"musl/src/math/__tanl.c",	798	"musl/src/math/__tanl.c",