lagoon: fix %mod jet to C-fmod truncation + NaN on divide-by-zero#55
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Both vendored jet variants (lagoon/vere standard + lagoon/vere64 64-bit) had the %mod ray-op and mod-scalar jets rounding the quotient to nearest (IEEE remainder) and returning the dividend on a zero divisor, diverging from the Hoon +mod (C fmod: truncate toward zero; NaN on /0 or a non-finite operand). Truncate the quotient with softfloat_round_minMag and return the width's qNaN on a non-finite quotient, in both u3qi_la_mod_i754 and u3qi_la_mods_i754, all four widths. Mirrors Vere PR #1022, verified on the live ~tex ship (5 mod 3 -> 2.0; 5 mod 0 -> NaN; f32 and f64). Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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The vendored
%modjets diverged from the Hoon+mod(fixed Hoon-side in #52 /sigilante/fix-i754-mod): they rounded the quotient to nearest (IEEE remainder) and returned the dividend on a zero divisor, where+moddoes Cfmod— truncate the quotient toward zero, and return NaN on a zero divisor or non-finite operand.This fixes both vendored jet variants:
lagoon/vere/noun/jets/i/lagoon.c(standard;maroon/...symlinks here)lagoon/vere64/noun/jets/lagoon.c(64-bit)In both
u3qi_la_mod_i754(ray-mod) andu3qi_la_mods_i754(mod-scalar), all four widths (f16/f32/f64/f128):softfloat_round_minMaginstead of the active mode.Purely SoftFloat-level (
f*_to_i64's mode is an explicit arg), so the stateless SoftBLAS interface is untouched.Verification
The 64-bit variant of this fix is Vere PR urbit/vere#1022, verified on a live ship (
~tex):5 mod 3(f64)2.0-1.05 mod 0(f64)NaN5.05 mod 32.05 mod 0NaN5.05 mod 3(f32)2.0-1.0🤖 Generated with Claude Code