libzigc: implement modff

`modf` function was generalized and renamed to `modfGeneric`, `modf` and
`modff` provide the appropriate type while calling that function. The
unit tests were also generalized so they can be reused for different
float types.

Both `modf` and `modff` were tested after making these changes:
```
$ stage4/bin/zig build test-libc -Dlibc-test-path=<LIBC-TEST-PATH> -Dtest-filter=modf -fqemu -fwasmtime --summary line
Build Summary: 921/921 steps succeeded
```

```
stage4/bin/zig build test-libc -Dlibc-test-path=<LIBC-TEST-PATH> -Dtest-filter=modff -fqemu -fwasmtime --summary line
Build Summary: 369/369 steps succeeded
```

lib/c/math.zig

@@ -4,6 +4,7 @@ const std = @import("std");
 const math = std.math;
 const expect = std.testing.expect;
 const expectEqual = std.testing.expectEqual;
+const expectApproxEqAbs = std.testing.expectApproxEqAbs;
 const expectApproxEqRel = std.testing.expectApproxEqRel;
 
 const symbol = @import("../c.zig").symbol;
@@ -37,6 +38,7 @@ comptime {
         symbol(&coshf, "coshf");
         symbol(&hypotf, "hypotf");
         symbol(&hypotl, "hypotl");
+        symbol(&modff, "modff");
         symbol(&nan, "nan");
         symbol(&nanf, "nanf");
         symbol(&nanl, "nanl");
@@ -166,66 +168,88 @@ fn isnanl(x: c_longdouble) callconv(.c) c_int {
     return if (math.isNan(x)) 1 else 0;
 }
 
-fn modf(x: f64, iptr: *f64) callconv(.c) f64 {
+fn modfGeneric(comptime T: type, x: T, iptr: *T) T {
     if (math.isNegativeInf(x)) {
-        iptr.* = -math.inf(f64);
+        iptr.* = -math.inf(T);
         return -0.0;
     }
 
     if (math.isPositiveInf(x)) {
-        iptr.* = math.inf(f64);
+        iptr.* = math.inf(T);
         return 0.0;
     }
 
     // Avoids raising the INVALID flag on qemu-riscv
     if (math.isNan(x)) {
-        iptr.* = math.nan(f64);
-        return math.nan(f64);
+        iptr.* = math.nan(T);
+        return math.nan(T);
     }
 
     const r = math.modf(x);
     iptr.* = r.ipart;
 
-    // If the result would be a negative zero, we must be explicit about
+    // If the result is a negative zero, we must be explicit about
     // returning a negative zero.
     return if (math.isNegativeZero(x) or (x < 0.0 and x == r.ipart)) -0.0 else r.fpart;
 }
 
-test "modf" {
-    var int: f64 = undefined;
-    const iptr = &int;
-    const eps_val = 1e-6;
+fn modf(x: f64, iptr: *f64) callconv(.c) f64 {
+    return modfGeneric(f64, x, iptr);
+}
 
-    const normal_frac = modf(1234.5678, iptr);
-    try expectApproxEqRel(0.5678, normal_frac, eps_val);
-    try expectApproxEqRel(1234.0, iptr.*, eps_val);
+fn modff(x: f32, iptr: *f32) callconv(.c) f32 {
+    return modfGeneric(f32, x, iptr);
+}
+
+fn testModf(comptime T: type) !void {
+    // Choose the appropriate `modf` impl to test based on type
+    const f = switch (T) {
+        f64 => modf,
+        f32 => modff,
+        else => @compileError("modf not implemented for " ++ @typeName(T)),
+    };
+
+    var int: T = undefined;
+    const iptr = &int;
+    const eps_val: comptime_float = @max(1e-6, math.floatEps(T));
+
+    const normal_frac = f(@as(T, 1234.567), iptr);
+    // Account for precision error
+    const expected = 1234.567 - @as(T, 1234);
+    try expectApproxEqAbs(expected, normal_frac, eps_val);
+    try expectApproxEqRel(@as(T, 1234.0), iptr.*, eps_val);
 
     // When `x` is a NaN, NaN is returned and `*iptr` is set to NaN
-    const nan_frac = modf(math.nan(f64), iptr);
+    const nan_frac = f(math.nan(T), iptr);
     try expect(math.isNan(nan_frac));
     try expect(math.isNan(iptr.*));
 
     // When `x` is positive infinity, +0 is returned and `*iptr` is set to
     // positive infinity
-    const pos_zero_frac = modf(math.inf(f64), iptr);
+    const pos_zero_frac = f(math.inf(T), iptr);
     try expect(math.isPositiveZero(pos_zero_frac));
     try expect(math.isPositiveInf(iptr.*));
 
     // When `x` is negative infinity, -0 is returned and `*iptr` is set to
     // negative infinity
-    const neg_zero_frac = modf(-math.inf(f64), iptr);
+    const neg_zero_frac = f(-math.inf(T), iptr);
     try expect(math.isNegativeZero(neg_zero_frac));
     try expect(math.isNegativeInf(iptr.*));
 
     // Return -0 when `x` is a negative integer
-    const nz_frac = modf(-1000.0, iptr);
+    const nz_frac = f(@as(T, -1000.0), iptr);
     try expect(math.isNegativeZero(nz_frac));
-    try expectEqual(-1000.0, iptr.*);
+    try expectEqual(@as(T, -1000.0), iptr.*);
 
     // Return +0 when `x` is a positive integer
-    const pz_frac = modf(1000.0, iptr);
+    const pz_frac = f(@as(T, 1000.0), iptr);
     try expect(math.isPositiveZero(pz_frac));
-    try expectEqual(1000.0, iptr.*);
+    try expectEqual(@as(T, 1000.0), iptr.*);
+}
+
+test "modf" {
+    try testModf(f64);
+    try testModf(f32);
 }
 
 fn nan(_: [*:0]const c_char) callconv(.c) f64 {

lib/libc/mingw/math/modff.c

@@ -1,42 +0,0 @@
-/**
- * This file has no copyright assigned and is placed in the Public Domain.
- * This file is part of the mingw-w64 runtime package.
- * No warranty is given; refer to the file DISCLAIMER.PD within this package.
- */
-#include <fenv.h>
-#include <math.h>
-#include <errno.h>
-
-float
-modff (float value, float* iptr)
-{
-  float int_part = 0.0F;
-  /* truncate */ 
-  /* truncate */
-#if (defined(_AMD64_) && !defined(_ARM64EC_)) || (defined(__x86_64__) && !defined(__arm64ec__))
-  asm volatile ("subq $8, %%rsp\n"
-    "fnstcw 4(%%rsp)\n"
-    "movzwl 4(%%rsp), %%eax\n"
-    "orb $12, %%ah\n"
-    "movw %%ax, (%%rsp)\n"
-    "fldcw (%%rsp)\n"
-    "frndint\n"
-    "fldcw 4(%%rsp)\n"
-    "addq $8, %%rsp\n" : "=t" (int_part) : "0" (value) : "eax"); /* round */
-#elif defined(_X86_) || defined(__i386__)
-  asm volatile ("push %%eax\n\tsubl $8, %%esp\n"
-    "fnstcw 4(%%esp)\n"
-    "movzwl 4(%%esp), %%eax\n"
-    "orb $12, %%ah\n"
-    "movw %%ax, (%%esp)\n"
-    "fldcw (%%esp)\n"
-    "frndint\n"
-    "fldcw 4(%%esp)\n"
-    "addl $8, %%esp\n\tpop %%eax\n" : "=t" (int_part) : "0" (value) : "eax"); /* round */
-#else
-  int_part = truncf(value);
-#endif
-  if (iptr)
-    *iptr = int_part;
-  return (isinf (value) ?  0.0F : value - int_part);
-}

lib/libc/musl/src/math/modff.c

@@ -1,34 +0,0 @@
-#include "libm.h"
-
-float modff(float x, float *iptr)
-{
-	union {float f; uint32_t i;} u = {x};
-	uint32_t mask;
-	int e = (int)(u.i>>23 & 0xff) - 0x7f;
-
-	/* no fractional part */
-	if (e >= 23) {
-		*iptr = x;
-		if (e == 0x80 && u.i<<9 != 0) { /* nan */
-			return x;
-		}
-		u.i &= 0x80000000;
-		return u.f;
-	}
-	/* no integral part */
-	if (e < 0) {
-		u.i &= 0x80000000;
-		*iptr = u.f;
-		return x;
-	}
-
-	mask = 0x007fffff>>e;
-	if ((u.i & mask) == 0) {
-		*iptr = x;
-		u.i &= 0x80000000;
-		return u.f;
-	}
-	u.i &= ~mask;
-	*iptr = u.f;
-	return x - u.f;
-}

src/libs/mingw.zig

@@ -977,7 +977,6 @@ const mingw32_x86_src = [_][]const u8{
 
 const mingw32_x86_32_src = [_][]const u8{
     // ucrtbase
-    "math" ++ path.sep_str ++ "modff.c",
     "math" ++ path.sep_str ++ "powf.c",
     "math" ++ path.sep_str ++ "sinhf.c",
     "math" ++ path.sep_str ++ "tanhf.c",

src/libs/musl.zig

@@ -934,7 +934,6 @@ const src_files = [_][]const u8{
     "musl/src/math/__math_uflowf.c",
     "musl/src/math/__math_xflow.c",
     "musl/src/math/__math_xflowf.c",
-    "musl/src/math/modff.c",
     "musl/src/math/modfl.c",
     "musl/src/math/nearbyint.c",
     "musl/src/math/nearbyintf.c",

src/libs/wasi_libc.zig

@@ -755,7 +755,6 @@ const libc_top_half_src_files = [_][]const u8{
     "musl/src/math/__math_uflowf.c",
     "musl/src/math/__math_xflow.c",
     "musl/src/math/__math_xflowf.c",
-    "musl/src/math/modff.c",
     "musl/src/math/modfl.c",
     "musl/src/math/nearbyintl.c",
     "musl/src/math/nextafter.c",